# Spectral Energy Distributions and Age Estimates of 39 Globular Clusters in
M31

Jun Ma,11affiliation: National Astronomical Observatories, Chinese Academy of
Sciences, Beijing, 100012, P. R. China;
<EMAIL_ADDRESS>Zhou Fan,11affiliation: National Astronomical
Observatories, Chinese Academy of Sciences, Beijing, 100012, P. R. China;
<EMAIL_ADDRESS>22affiliation: Graduate University, Chinese Academy
of Sciences, Beijing, 100039, P. R. China Richard de Grijs,33affiliation:
Department of Physics & Astronomy, The University of Sheffield, Hicks
Building, Hounsfield Road, Sheffield S3 7RH, UK 11affiliation: National
Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012, P.
R. China;
<EMAIL_ADDRESS>Zhenyu Wu,11affiliation: National Astronomical
Observatories, Chinese Academy of Sciences, Beijing, 100012, P. R. China;
<EMAIL_ADDRESS>Xu Zhou,11affiliation: National Astronomical
Observatories, Chinese Academy of Sciences, Beijing, 100012, P. R. China;
<EMAIL_ADDRESS>Jianghua Wu,11affiliation: National Astronomical
Observatories, Chinese Academy of Sciences, Beijing, 100012, P. R. China;
<EMAIL_ADDRESS>Zhaoji Jiang,11affiliation: National Astronomical
Observatories, Chinese Academy of Sciences, Beijing, 100012, P. R. China;
<EMAIL_ADDRESS>and Jiansheng Chen11affiliation: National
Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012, P.
R. China;
<EMAIL_ADDRESS>
###### Abstract

This paper supplements Jiang et al. (2003), who studied 172 M31 globular
clusters (GCs) and globular cluster candidates from Battistini et al. (1987)
on the basis of integrated photometric measurements in the Beijing-Arizona-
Taiwan-Connecticut (BATC) photometric system. Here, we present multicolor
photometric CCD data (in the BATC system) for the remaining 39 M31 GCs and
candidates. In addition, the ages of 35 GCs are constrained by comparing our
accurate photometry with updated theoretical stellar synthesis models. We use
photometric measurements from GALEX in the far- and near-ultraviolet and 2MASS
infrared $JHK_{s}$ data, in combination with optical photometry. Except for
two clusters, the ages of the other sample GCs are all older than 1 Gyr. Their
age distribution shows that most sample clusters are younger than 6 Gyr, with
a peak at $\sim 3$ Gyr, although the ‘usual’ complement of well-known old GCs
(i.e., GCs of similar age as the majority of the Galactic GCs) is present as
well.

###### Subject headings:

galaxies: individual (M31) – galaxies: star clusters – galaxies: stellar
content

††slugcomment: AJ, in press

##  1\. Introduction

The process of galaxy formation and evolution ranks among the most important
outstanding problems in astrophysics (e.g., Perrett et al., 2002). One way to
better understand the underlying questions is by studying globular clusters
(GCs). GCs are often considered the fossils of the galaxy formation process,
since they tend to form in the very early stage of their host galaxy’s
evolution (Barmby et al., 2000). A GC is a densely packed, gravitationally
bound, roughly spherical system of several thousand to about one million
stars. They can be observed out to great distances, which implies that they
can be used to study and probe the properties of extragalactic systems. The
most distant GC systems studied to date are located in the Coma Cluster; their
study has been facilitated by Hubble Space Telescope (HST) Wide Field and
Planetary Camera-2 (WFPC2) observations (Baum et al., 1995; Kavelaars et al.,
2000; Harris et al., 2000; Woodworth & Harris, 2000).

M31 (NGC 224), the Andromeda galaxy, is an early-type spiral galaxy (type Sb),
located at a distance of $\sim 780$ kpc (Stanek & Garnavich, 1998; Macri,
2001). It is the nearest and largest spiral galaxy in the Local Group of
galaxies and has been the subject of many GC studies and surveys. Hubble
(1932) first discovered 140 GC candidates characterized by $m_{\rm pg}\leq 18$
mag. Subsequently, a number of studies (Seyfert & Nassau, 1945; Hiltner, 1958;
Mayall & Eggen, 1953; Kron & Mayall, 1960) identified $\sim 160$ GC candidates
in M31. Vetes̆nik (1962) compiled the first major M31 GC catalog, containing
about 300 GC candidates and including $UBV$ photometric data. The most
extensive GC surveys have since been published by Sargent et al. (1977),
Crampton et al. (1985), and the Bologna group (Battistini et al., 1980, 1987,
1993). In particular, Crampton et al. (1985) and Battistini et al. (1980,
1987, 1993) provided photometric data in either $UBV$ or $UBVR$. These surveys
were mostly based on visual searches of photographic plates and are fairly
complete down to $V=18$ mag ($M_{V}\sim-6.5$ mag) (Fusi Pecci et al., 1993),
although a number of recent studies searched for fainter GCs in M31 (e.g.,
Mochejska et al., 1998; Barmby & Huchra, 2001; Kim et al., 2007). However,
Galleti et al. (2006) showed that a significant number of class-D and E GCs
with $V\gtrsim 17$ are still to be confirmed (and hence the GC luminosity
function is incomplete), and that large surveys are needed to reach a complete
sample of M31 GCs. Following on from the first extensive spectroscopic survey
of M31 GCs by van den Bergh (1969), a significant number of authors (e.g.,
Huchra et al., 1982, 1991; Dubath & Grillmair, 1997; Federici et al., 1993;
Jablonka et al., 1998; Barmby et al., 2000; Perrett et al., 2002; Galleti et
al., 2006; Lee et al., 2008, and references therein) embarked on studies of
their spatial, kinematic, and metal-abundance properties. The first
comprehensive catalog including photometric and spectroscopic data for M31 GCs
was assembled by Barmby et al. (2000). The Revised Bologna Catalog (RBC) of
M31 GCs was recently published by Galleti et al. (2004) and has since been
revised a number of times (Galleti et al., 2005, 2006, 2007). In the primary
catalog (Galleti et al., 2004), all known M31 GCs and candidates were compiled
based on a literature survey, leading to a total of 1164 entries including 337
confirmed GCs, 688 GC candidates, and 10 objects with undetermined
classification. In addition, Galleti et al. (2004) identified 693 known and
candidate GCs in M31 using the 2MASS database and included their 2MASS
$JHK_{s}$ magnitudes. The latest RBC (V3.5) was updated on March 27, 2008, and
includes the newly discovered star clusters from Mackey et al. (2006), Kim et
al. (2007), and Huxor et al. (2008). In total, 1567 GCs and GC candidates (509
confirmed GCs and 1058 GC candidates) are known in M31; 421 former GC
candidates turned out to be stars, asterisms, galaxies, Hii regions, or
extended clusters. In addition, the RBC V3.5 includes photometric data of M31
GCs and GC candidates in the far- and near-ultraviolet (FUV and NUV) from the
Nearby Galaxies Survey (NGS) of the Galaxy Evolution Explorer (GALEX) (Rey et
al., 2007). Very recently, Caldwell et al. (2009) presented a new catalog of
670 likely star clusters in the field of M31, all with updated high-quality
coordinates accurate to $0.2^{\prime\prime}$, based on images from either the
Local Group Survey (Massey, 2006) or the Digital Sky Survey.

An accurate and reliable analysis of integrated stellar populations (such as
star clusters) is key to understanding the formation and evolutionary process
in galaxies. By means of comparisons of integrated populations with models of
homogeneous stellar systems, i.e., simple stellar populations (SSPs), recent
studies have achieved some success in determining ages and masses for
extragalactic star clusters (e.g., de Grijs et al., 2003a, b, c; Bik et al.,
2003; Ma et al., 2006; Fan et al., 2006; Ma et al., 2007).

Ma et al. (2006) and Fan et al. (2006) derived age estimates for M31 GCs by
fitting SSP models (Bruzual & Charlot, 2003, henceforth BC03) to their
photometric measurements in a large number of intermediate- and broad-band
passbands from the optical to the near-infrared (NIR). For instance, Ma et al.
(2007) constrained the age of the M31 GC S312 (B379), using multicolor
photometry from the NUV to the NIR, to $9.5^{+1.15}_{-0.99}$ Gyr. S312 (B379)
is among the first extragalactic GCs for which the age was estimated
accurately using main-sequence photometry, i.e., Brown et al. (2004) estimated
its age at $10^{+2.5}_{-1}$ Gyr. This was based on their analysis of the
cluster’s color-magnitude diagram (CMD) below the main-sequence turn-off
(MSTO) using extremely deep images obtained with the Advanced Camera for
Surveys (ACS) on board the HST. They performed a quantitative comparison of
their resolved stellar photometry with the isochrones of VandenBerg et al.
(2006).

In this paper we first describe our new observations and the relevant data-
processing steps, as well as the complementary data used from the literature
(§2). In §3 we quantitatively compare the spectral energy distributions (SEDs)
of the GCs in our sample with the galev SSP models. Finally, our results and a
summary are presented in §4.

##  2\. Database

###  2.1. The sample

The GC sample used in this paper was taken from the Bologna catalog of
Battistini et al. (1987), which contains 827 M31 GCs and GC candidates. In
addition, our sample also supplements that of Jiang et al. (2003), who studied
172 GC candidates from Battistini et al. (1987) on the basis of integrated
photometric measurements in the Beijing-Arizona-Taiwan-Connecticut (BATC)
photometric system. In Jiang et al. (2003), all GC candidates of classes A and
B (353 objects) in Battistini et al. (1987) (i.e., their Table IV) were
adopted as their original sample. However, of these only 223 objects are in
their observed CCD fields. They also noted that B007 is a galaxy, and B055,
B132 and B147 are virtually stars (Barmby et al., 2000). These four objects
were therefore not included in Jiang et al. (2003)’s final sample. In summary,
219 class-A or B GCs were observed by Jiang et al. (2003), of which 47 were
excluded because of missing photometric measurements in some filters. In this
paper we analyze these 47 GC candidates on the basis of newly observed data in
the BATC photometric system combined with GALEX FUV/NUV photometry, broad-band
$UBVRI$, and NIR $JHK_{s}$ (2MASS) data. However, we did not manage to obtain
accurate photometric measurements for a number of objects because of either
the dominance of a nearby very bright object (B095, B176, and B202), the GC
candidate being very faint and superimposed on a very high background (B119
and B324), or the GC candidate being located near M32 (B124) or NGC 205
(B331), both also resulting in a very high contribution. In addition, object
B330 is faint and located very close to a brighter object, rendering accurate
photometry impossible. Thus, here we analyze the multicolor photometric
properties of 39 GC candidates. Figure 1 shows the spatial distributions of
both our sample GCs (circles) and the Jiang et al. (2003) GCs (plus signs)
across the M31 field.

Figure 1.— Spatial distribution of the GC candidates in M31. Circles and plus
signs represent the samples discussed in this paper and by Jiang et al.
(2003), respectively. The large ellipse is the M31 disk/halo boundary as
defined by Racine (1991); the two small ellipses are the $D_{25}$ isophotes of
NGC 205 (northwest) and M32 (southeast).

###  2.2. Observations and data reduction

To obtain photometric measurements in the BATC photometric system for the 39
GC candidates for which Jiang et al. (2003) did not obtain photometry in a
number of filters, we re-observed the objects. The BATC photometric system
uses a Ford Aerospace 2048$\times$2048 CCD camera with a pixel size of 15
$\mu$m, mounted at the focus of the 0.6/0.9m $f$/3 Schmidt telescope at
Xinglong Station (National Astronomical Observatories of China; NAOC). The CCD
field of view is $58^{\prime}\times 58^{\prime}$, with a pixel size of
$1.7^{\prime\prime}$. The multicolor BATC filter system includes 15
intermediate-band filters covering the wavelength range from 3300Å to 1
$\mu$m. These filters were specifically designed to avoid contamination from
the brightest and most variable night-sky emission lines. The CCD camera is
not sensitive at the shortest wavelengths covered by the BATC filters. For
this reason, neither Jiang et al. (2003) nor we used the two bluest filters
($a$ and $b$) for our observations. Finding charts of the sample GCs and GC
candidates in the BATC $g$ band (centered at 5795Å), obtained with the NAOC
60/90cm Schmidt telescope, are shown in Fig. 2.

Thirteen hours of imaging of the M31 field of Jiang et al. (2003) were
obtained through the usable set of 13 intermediate-band filters from November
15, 2003 to December 13, 2003. Bias subtraction and flat fielding using dome
flats were done with the BATC automatic data-reduction software, pipeline i,
originally developed for the BATC Multicolor Sky Survey (Fan et al., 1996;
Zheng et al., 1999). The dome flat-field images were taken using a diffuser
plate in front of the Schmidt telescope’s corrector plate. This flat-fielding
technique was verified using photometry obtained for other galaxies and
spectrophotometric observations (see, e.g., Fan et al., 1996; Zheng et al.,
1999; Wu et al., 2002; Yan et al., 2000; Zhou et al., 2001, 2004).
Spectrophotometric calibration of the M31 images was done by observations of
four F-type subdwarfs, HD 19445, HD 84937, BD ${+26^{\circ}2606}$, and BD
${+17^{\circ}4708}$ (Oke & Gunn, 1983). Our magnitudes are therefore defined
in the spectrophotometric AB magnitude system (i.e., the Oke & Gunn
$\tilde{f_{\nu}}$ monochromatic system),

$m_{\rm BATC}=-2.5{\rm log}\tilde{F_{\nu}}-48.60,$ (1)

where $\tilde{F_{\nu}}$ is the appropriately averaged monochromatic flux in
units of erg s-1 cm-2 Hz-1 at the effective wavelength of the specific
passband. In the BATC system $\tilde{F_{\nu}}$ is defined as (Yan et al.,
2000)

$\tilde{F_{\nu}}=\frac{\int{\rm d}({\rm log}\nu)f_{\nu}r_{\nu}}{\int{\rm
d}({\rm log}\nu)r_{\nu}},$ (2)

which relates the magnitude to the number of photons detected rather than to
the input flux (Fukugita et al., 1996). In Eq. (2), $r_{\nu}$ is the system’s
response and $f_{\nu}$ the object’s SED. Spectrophotometric calibration of the
M31 images using the Oke-Gunn standard stars was done during photometric
nights (see for details Yan et al., 2000; Zhou et al., 2001). Using these
standard-star images, we iteratively obtained atmospheric extinction curves
and the variation of these extinction coefficients as a function of the time
of night (cf. Yan et al., 2000; Zhou et al., 2001),

$m_{\rm BATC}=m_{\rm inst}+[K+\Delta K({\rm UT})]X+C,$ (3)

where $X$ is the airmass and $[K+\Delta K({\rm UT})]$ the time-dependent
extinction term. The instrumental magnitudes ($m_{\rm inst}$) of selected
bright, isolated, and unsaturated stars on the M31 images observed on
photometric nights can be readily transformed to the BATC system ($m_{\rm
BATC}$). The calibrated magnitudes of these stars were then used as secondary
standards to uniformly combine images from calibrated nights with their
counterparts observed on non-photometric nights. Table 1 lists the parameters
of the BATC filters and the observational statistics; column 6 provides the
scatter, in magnitudes, for the photometric observations of the four primary
standard stars in each filter.

Figure 2.— Finding charts of the sample GCs and GC candidates in the BATC $g$
band, obtained with the NAOC 60/90cm Schmidt telescope. The field of view of
each image is $11^{\prime}\times 11^{\prime}$.

###  2.3. Integrated photometry

For each M31 GC candidate we used the phot routine in DAOPHOT (Stetson, 1987)
to obtain the integrated photometry. To avoid contamination from nearby
objects, we adopted an aperture of $10.2^{\prime\prime}$ diameter,
corresponding to 6 pixels. Inner and outer radii for background determination
were taken at 8 and 13 pixels from the GC center. Given the small aperture
used for the GC observations, aperture corrections were determined as follows.
We used isolated stars to determine the magnitude difference between diameter
of 6 pixels and the fully integrated magnitude of these stars in each of the
13 BATC filters used. The SEDs for our sample of 39 GCs and GC candidates were
then corrected for the filter-specific differences, and these values are given
in Table 2. Columns 2–14 give the magnitudes in the 13 BATC passbands used for
our observations. For each object the second line lists the $1\sigma$
uncertainties in magnitude for the corresponding passband. The errors for each
filter are given by DAOPHOT. The magnitudes of B129 in the $c$ and $d$
filters, and that of B195 in $p$ filter could not be obtained owing to low
signal-to-noise ratios in these filters.

###  2.4. GALEX, broad-band, and 2MASS photometry

To estimate the ages of the M31 sample GCs and GC candidates accurately, we
use as many photometric data points covering as wide a wavelength range as
possible (cf. de Grijs et al., 2003b; Anders et al., 2004). In addition,
Kaviraj et al. (2007) showed that the combination of FUV and NUV photometry
with optical observations in the standard broad bands enables one to
efficiently break the age-metallicity degeneracy. Worthey (1994) showed that
the age-metallicity degeneracy associated with optical broad-band colors is
$\Delta{\rm age}/\Delta Z\sim 3/2$ (see also MacArthur et al., 2004). However,
de Jong (1996) showed that this degeneracy can be partially broken by adding
NIR photometry to optical colors, which was recently confirmed by Wu et al.
(2005). Cardiel et al. (2003) found that the inclusion of an infrared (IR)
passband can improve the predictive power of the stellar population
diagnostics by $\sim 30$ times compared to using optical photometry alone.
Since NIR photometry is less sensitive to interstellar extinction than the
classical optical passbands, Kissler-Patig et al. (2002) and Puzia et al.
(2002) also suggested that it provides useful complementary information that
can help to disentangle the age-metallicity degeneracy (also see Galleti et
al., 2004).

Rey et al. (2007) published GALEX NUV and FUV photometric data for 485 and 273
M31 GCs, respectively. The photometric data for 28 (NUV) and 17 (FUV) of our
M31 sample GCs in common is listed in Table 3\. Again, for each object the
second line lists the photometric uncertainties for the corresponding
passband. The GALEX photometric system is calibrated to match the
spectrophotometric AB system.

To date, the study of M31 GCs has been largely based on the excellent Bologna
catalog (Battistini et al., 1980, 1987, 1993). Updates to the original RBC
were provided by Galleti et al. (2004) who take as their photometric reference
the dataset of Barmby et al. (2000) in order to obtain the most homogeneous
set of photometric measurements available. Barmby et al. (2000) published
optical and IR photometric data for 285 M31 GCs (see their Table 3), obtained
with the 4-Shooter CCD mosaic camera and the SAO IR imager on the 1.2m
telescope at the Fred Lawrence Whipple Observatory. Photometric measurements
in the $UBVRI$ bands were published by Barmby et al. (2000) for most of our
sample objects. Therefore, we preferentially adopt the $UBVRI$ measurements of
Barmby et al. (2000). For the remaining GCs we follow Galleti et al. (2004),
who updated the Bologna catalog with homogenised optical ($UBVRI$) photometry
collected from the most recent photometric references available. Galleti et
al. (2004) did not include the photometric uncertainties. Although we refer to
the original papers, the uncertainties associated with the same object but
based on the use of different photometric systems are often very different. In
addition, Galleti et al. (2004) transformed their $UBVRI$ photometry to the
reference system of Barmby et al. (2000) by applying offsets derived from
objects in common between the relevant catalog and the data set of Barmby et
al. (2000). The measurements are therefore internally consistent, and
referencing the original uncertainties may be irrelevant. Therefore, we only
adopted photometric uncertainties as suggested by Galleti et al. (2004), i.e.,
0.05 mag in $BVRI$ and 0.08 mag in $U$. In fact, these photometric
uncertainties do not affect our results significantly, as we showed in Fan et
al. (2006) (see their §4.3 for details).

Galleti et al. (2004) identified 693 known and candidate GCs in M31 using the
2MASS database, and determined their 2MASS $JHK_{s}$ photometric magnitudes
(transformed to the CIT photometric system) (Elias et al., 1982, 1983).
However, we need the original 2MASS $JHK_{s}$ magnitudes for our sample GCs to
compare our observational SEDs with the SSP models, so we reversed this
transformation using the same procedures. Since Galleti et al. (2004) did not
provide the 2MASS $JHK_{s}$ uncertainties, we obtained these by comparing the
photometric magnitudes with Fig. 2 of Carpenter et al. (2001). They show the
observed photometric rms uncertainties as a function of magnitude for stars
brighter than their observational completeness limits. We include the broad-
band and 2MASS photometry (and the associated uncertainties) of the sample GCs
in Table 3. We also list the new classification flags, following RBC V3.5
notation. From Table 3 we learn that B052 and B062 are classified as galaxies
based on their radial velocities. We will therefore not estimate their ages
below.

###  2.5. Comparison with previously published photometry

The BATC intermediate-band system can easily be transformed to the $UBVRI$
broad-band system. Zhou et al. (2003) derived the relationships between these
two systems using standard stars from the catalogs of Landolt (1983, 1992) and
Galadí-Enríquez et al. (2000):

$m_{B}=m_{d}+0.2201(m_{c}-m_{e})+0.1278\pm 0.076,$ (4)

$m_{V}=m_{g}+0.3292(m_{f}-m_{h})+0.0476\pm 0.027.$ (5)

To check our photometry we derived the magnitudes in $B$ and $V$ based on Eqs.
(4) and (5). We transformed the magnitudes of our 39 GCs and GC candidates in
the BATC $c,d$, $e$ bands to $B$-band photometry, and BATC $f,g$, and $h$-band
measurements into $V$-band data. Fig. 3 shows a comparison of our $V$ and
$(B-V)$ photometry with previously published measurements of Barmby et al.
(2000) and Galleti et al. (2004). The mean $V$ magnitude and $(B-V)$ color
differences (in the sense of this paper minus Barmby et al. (2000) or Galleti
et al. (2004)) are $\langle\Delta V\rangle=-0.066\pm 0.013$ mag and
$\langle\Delta(B-V)\rangle=-0.040\pm 0.017$ mag, respectively, thus showing
excellent agreement.

Figure 3.— Comparison of our newly obtained cluster photometry with previous
measurements by Barmby et al. (2000) (triangles) and Galleti et al. (2004)
(crosses). The dashed lines enclose $\pm 0.2$ mag in $V$ and $\pm 0.3$ mag in
$B-V$.

###  2.6. Metallicities and reddening values

To estimate the ages of our sample GCs accurately we required that our GCs
have both independently determined metallicities and reddening values. We used
three homogeneous sources for spectroscopic metallicities (Huchra et al.,
1991; Barmby et al., 2000; Perrett et al., 2002) and one reference (Fan et
al., 2008).

Huchra et al. (1991) obtained spectroscopy of 150 M31 GCs and candidates with
the Multiple Mirror Telescope (MMT). The system they used has a resolution of
8–9Å and enhanced blue sensitivity. To obtain many of the strongest and most
metallicity-sensitive spectral features of interest in the ultraviolet, they
extended their observations to the atmospheric cut-off at 3200Å (see details
in Brodie & Huchra, 1990). The metallicities of these 150 objects were
determined using six absorption-line indices from integrated cluster spectra
employing the method of Brodie & Huchra (1990).

Barmby et al. (2000) observed 61 M31 GCs and candidates spectroscopically
using the Keck Low Resolution Imaging Spectrometer (LRIS) and the MMT Blue
Channel spectrograph. With Keck LRIS, they used a 600 $\ell$ mm-1 grating with
a 1.2Å pixel-1 dispersion from 3670–6200Å, and a resolution of 4–5Å. With the
MMT Blue Channel, they used a 300 $\ell$ mm-1 grating with a 3.2Å pixel-1
dispersion from 3400–7200 Å, and a resolution of 9–11Å. They obtained the
cluster metallicities on the basis of the Brodie & Huchra (1990) method as
well.

Perrett et al. (2002) determined metallicities for more than 200 M31 GCs and
candidates using the Wide Field Fibre Optic Spectrograph (WYFFOS) at the 4.2m
William Herschel Telescope. Their spectral range covers $\sim$ 3700–5600Å
using two gratings, one of which (H2400B, 2400 $\ell$ mm-1) yields a
dispersion of 0.8Å pixel-1 and a spectral resolution of 2.5Å over the range
3700–4500Å, and the other (R1200R, 1200 $\ell$ mm-1) yields a dispersion of
1.5Å pixel-1 and a spectral resolution of 5.1Å over the range 4400–5600Å.
Perrett et al. (2002) calculated 12 absorption-line indices, again using the
method of Brodie & Huchra (1990). Through a comparison of the line indices
with published M31 GC [Fe/H] values from previous studies (Bònoli et al.,
1987; Brodie & Huchra, 1990; Barmby et al., 2000), they found that the line
indices of the CH (G band), Mg$b$, and Fe53 lines best represented their
observed GCs. Therefore, Perrett et al. (2002) determined the metallicities of
their sample targets using an unweighted mean of these three [Fe/H] values.

Using metallicities from the literature (Huchra et al., 1991; Barmby et al.,
2000; Perrett et al., 2002) combined with the RBC, Fan et al. (2008)
determined 443 reddening values and intrinsic colors, as well as 209
metallicities for individual clusters without spectroscopic observations.

To use all metallicities as coherently as possible we ranked the sources of
M31 GCs metallicities, choosing Perrett et al. (2002) metallicities whenever
available because of the large number of metallicity determinations.
Metallicities from Barmby et al. (2000) and Huchra et al. (1991) were
preferred if Perrett et al. (2002) determinations were not available. If
spectroscopic metallicities were missing, we used Fan et al. (2008).
Metallicities were not available for B089 and B226. As a consequence, we do
not attempt to determine their ages (see details in §4). The final set of
metallicities for the sample clusters is included in Table 4.

For the reddening values of the sample GCs we refer to Barmby et al. (2000)
and Fan et al. (2008). Barmby et al. (2000) determined the reddening for each
cluster using correlations between optical and IR colors and metallicity, and
by defining various ‘reddening-free’ parameters using their large database of
multicolor photometry. Barmby et al. (2000) found that the M31 and Galactic GC
extinction laws, and the M31 and Galactic GC color-metallicity relations are
similar. They estimated the reddening to M31 objects with spectroscopic data
using the relationship between intrinsic optical color and metallicity for
Galactic clusters. For objects without spectroscopic data they used the
relationships between the reddening-free parameters and certain intrinsic
colors based on Galactic GC data. Following the methods in Barmby et al.
(2000), Fan et al. (2008) (re-)determined reddening values for 443 clusters
and cluster candidates. We choose Fan et al. (2008) reddening values whenever
available because their reddening values comprise a homogeneous data set and
they are larger than those of Barmby et al. (2000). The reddening values for
the sample clusters are listed in Table 4. The values of extinction
coefficient $R_{\lambda}$ are obtained by interpolating the interstellar
extinction curve of Cardelli et al. (1989).

##  3\. Age determination

###  3.1. Stellar populations and synthetic photometry

The most direct method to constrain the ages of different stellar populations
involves comparing the observed luminosity levels of the MSTOs. Unfortunately,
this approach is limited to the nearest GCs, where individual stars can be
resolved and measured down to a few magnitudes fainter than the MSTO. Even in
M31, the nearest large spiral galaxy, the MSTO is only reached for one GC
(S312) (also see Brown et al., 2004; Rey et al., 2007; Ma et al., 2007).
However, since the pioneering work of Tinsley (1968, 1972) and Searle et al.
(1973) evolutionary population synthesis modeling has become a powerful tool
for the interpretation of integrated spectrophotometric observations of
galaxies as well as their components (see e.g. Anders et al., 2004).

In evolutionary synthesis models, SSPs are modeled on the basis of a
collection of evolutionary tracks of stars of different initial masses and a
set of stellar spectra at different evolutionary stages. To estimate the ages
of our sample GCs we compare their SEDs with the galev SSP models (e.g., Kurth
et al., 1999; Schulz et al., 2002; Anders & Fritze-v. Alvensleben, 2003). The
galev SSPs are based on the Padova isochrones (with the most recent versions
using the updated Bertelli et al. (1994) isochrones, which include the
thermally-pulsing asymptotic giant-branch [TP-AGB] phase), and a Salpeter
(1955) stellar initial mass function with a lower-mass limit of $0.10~{}{\rm
M}_{\odot}$ and the upper-mass limit between 50 and 70 ${\rm M}_{\odot}$,
depending on metallicity. The full set of models spans the wavelength range
from 91Å to 160 $\mu$m. These models cover ages from $4\times 10^{6}$ to
$1.6\times 10^{10}$ yr, with an age resolution of 4 Myr for ages up to 2.35
Gyr, and 20 Myr for greater ages.

Since our observational data consists of integrated luminosities through a
given set of filters, we convolved the theoretical SSP SEDs with the GALEX FUV
and NUV, broad-band $UBVRI$, BATC, and 2MASS $JHK_{s}$ filter response curves
to obtain synthetic ultraviolet, optical, and NIR photometry for comparison.
The synthetic magnitude in the AB magnitude system for the $i^{\rm th}$ filter
can be computed as

$m_{i}=-2.5\log\frac{\int_{\lambda}F_{\lambda}\varphi_{i}(\lambda){\rm
d}\lambda}{\int_{\lambda}\varphi_{i}(\lambda){\rm d}\lambda}-48.60,$ (6)

where $F_{\lambda}$ is the theoretical SED and $\varphi_{i}$ the response
curve of the $i^{\rm th}$ filter of the GALEX FUV/NUV, $UBVRI$, BATC, and
2MASS $JHK_{s}$ photometric systems. Here, $F_{\lambda}$ changes as a function
of age and metallicity.

###  3.2. Fitting results

We use a $\chi^{2}$ minimization test to examine which galev SSP models are
most compatible with the observed SEDs, following

$\chi^{2}=\sum_{i=1}^{23}{\frac{[m_{\lambda_{i}}^{\rm
intr}-m_{\lambda_{i}}^{\rm mod}(t)]^{2}}{\sigma_{i}^{2}}},$ (7)

where $m_{\lambda_{i}}^{\rm mod}(t)$ is the integrated magnitude in the
$i^{\rm th}$ filter of a theoretical SSP at age $t$, $m_{\lambda_{i}}^{\rm
intr}$ represents the intrinsic integrated magnitude in the same filter, and

$\sigma_{i}^{2}=\sigma_{{\rm obs},i}^{2}+\sigma_{{\rm mod},i}^{2}.$ (8)

Here, $\sigma_{{\rm obs},i}^{2}$ is the observational uncertainty, and
$\sigma_{{\rm mod},i}^{2}$ is the uncertainty associated with the model
itself, for the $i^{\rm th}$ filter. Charlot et al. (1996) estimated the
uncertainty associated with the term $\sigma_{{\rm mod},i}^{2}$ by comparing
the colors obtained from different stellar evolutionary tracks and spectral
libraries. Following Wu et al. (2005), Ma et al. (2006), and Fan et al. (2006)
we adopt $\sigma_{{\rm mod},i}^{2}=0.05$. In fact, the values $\sigma_{{\rm
mod},i}^{2}$ adopted do not change the best fits, but only affect the
$\chi^{2}$ values.

The galev SSP models include five initial metallicities,
$Z=0.0004,0.004,0.008,0.02$ (solar metallicity), and 0.05. Spectra for other
metallicities can be obtained by linear interpolation of the appropriate
spectra for any of these metallicities. In addition, if the metallicity of a
cluster is poorer than $Z=0.0004$, we only use the model of $Z=0.0004$. The
best fits to the SEDs of our GCs are presented in Fig. 4.

Figure 4.— Best-fitting integrated SEDs of the galev SSP models shown in
relation to the intrinsic SEDs for our sample GCs. The photometric data points
are represented by the symbols with error bars (vertical error bars for
uncertainties and horizontal ones for the approximate wavelength coverage of
each filter). Open circles represent the calculated magnitude of the model
SEDs for each filter.

Figure 4.— Continued.

##  4\. Results and summary

In the previous Section we determined the ages of 35 M31 GCs and GC
candidates. The results are listed in Table 5. The metallicity of B089 and
B226, and the reddening of B089 had not been determined previously. From Fig.
5, which shows the age distribution of the sample clusters (see also Table 5)
we conclude that, except for two clusters, the ages of the other sample GCs
are all older than 1 Gyr. Most sample GCs are younger than 6 Gyr, with a peak
at $\sim 3$ Gyr. The ‘usual’ complement of well-known old GCs (i.e., GCs of
similar age as the majority of the Galactic GCs) is also present.

Figure 5.— Age distribution of our sample GCs and GC candidates in M31.

As discussed in §2.6, to estimate the ages of our sample GCs accurately we
required that our GC sample have both independently determined metallicities
and reddening values. For metallicity, we used Huchra et al. (1991), Barmby et
al. (2000), and Perrett et al. (2002) as our reference data set. Since all of
these authors determined the M31 GC metallicities using the calibration of
Brodie & Huchra (1990), all three metallicity determinations are on the same
[Fe/H] scale and there are no systematic offsets among any of these data sets
(see details in Perrett et al., 2002). However, individual metallicity
differences exist, which may affect our age estimates. Twelve GCs and GC
candidates have two metallicity determinations, of which B004, B219, and B238
exhibit the largest differences ($>0.2$ dex). The metallicities of B004, B219,
and B238 from Perrett et al. (2002) are $-0.31\pm 0.74$, $-0.01\pm 0.57$, and
$-0.57\pm 0.66$ dex, compared to $-1.26\pm 0.59$, $-0.53\pm 0.53$, and
$-1.22\pm 0.76$ dex from Huchra et al. (1991). Large metallicity differences
lead to large age differences. The ages of B004, B219, and B238 are estimated
at $4.10\pm 0.55$, $2.50\pm 0.15$, and $5.00\pm 0.45$ Gyr (based on the
metallicities of Perrett et al., 2002), compared to $14.40\pm 0.75$, $11.60\pm
1.45$ and $14.40\pm 0.80$ Gyr (metallicities of Huchra et al., 1991). This
implies that the accuracy of the metallicity determinations is very important
for the corresponding age estimates. The age differences for the other 10 GCs
are less than 1 Gyr based on the metallicities of both Perrett et al. (2002)
and Huchra et al. (1991), except for B045: $8.80\pm 1.45$ Gyr versus $6.30\pm
0.45$ Gyr based on Perrett et al. (2002) and Huchra et al. (1991)
metallicities, respectively. In general, the three different sources of
spectroscopic metallicities provide homogeneous age estimates. For B004, B219,
and B238 the signal-to-noise ratios of the observations of Huchra et al.
(1991) and Perrett et al. (2002) are too low. High-quality spectral
observations of these three GCs are needed. In addition, we point out that the
metallicity calibration of Brodie & Huchra (1990) is solely based on old GCs.
However, the sample GCs and GC candidates discussed in this paper are
estimated to be young or of intermediate age, so that the age estimates may be
somewhat biased by the adopted calibration.

Barmby et al. (2000) discovered that M31 contains GCs exhibiting strong Balmer
lines and A-type spectra, from which one infers that these GCs must be very
young. Beasley et al. (2004) and Puzia et al. (2005) confirmed this conclusion
of Barmby et al. (2000). Burstein et al. (2004) and Fusi Pecci et al. (2005)
increased the sample of young M31 GCs to 67. Very recently, Caldwell et al.
(2009) determined the ages and reddening values of 140 young clusters in M31
by comparing the observed spectra with model spectra, and these clusters are
less than 2 Gyr old. Most have ages between $10^{8}$ and $10^{9}$ yr. The ages
of the M31 clusters determined in this paper are in agreement with previous
determinations.

Many M31 GCs are resolved in HST observations. Some authors, including Ajhar
et al. (1996), Fusi Pecci et al. (1996), Rich et al. (1996), Holland et al.
(1997), Jablonka et al. (2000), Williams & Hodge (2001a), Williams & Hodge
(2001b), and Rich et al. (2005), used WFPC2 images to construct CMDs for
determination of the clusters’ metallicities, reddening values, and ages.
However, these CMDs are usually not deep enough to show conspicuous MSTOs and
thus be useful for robust age determinations. In fact, only Williams & Hodge
(2001a) and Williams & Hodge (2001b) managed to estimate the ages for four
blue massive, compact star clusters and 79 candidate young star clusters by
fitting isochrones to the stellar photometry.

Our sample contains four GCs in common with Ajhar et al. (1996) (B006 and
B045), Fusi Pecci et al. (1996) (also B006 and B045), and Rich et al. (2005)
(B012 and B233). However, only B012 (Rich et al., 2005) could be older than
about 8 Gyr (see Gallart et al. 2005), given the presence of a prominent blue
horizontal branch, which compares rather poorly with the age obtained here
($\sim 2$ Gyr). However, even with multi-passband photometry spanning from the
FUV to $K_{s}$, we can only determine cluster ages in a statistical sense
(also see Gallagher & Grebel, 2002; de Grijs et al., 2005).

This discrepancy of a few Gyr highlights the difficulty of obtaining age
estimates of unresolved intermediate-age clusters based on multi-passband
photometry, given that the color evolution of SSPs is only minimally age
dependent once the population has reached an age of $\sim 1-3$ Gyr. In
addition, although the general age distribution of an entire cluster
population (in a given galaxy) can be retrieved fairly self-consistently, the
clusters’ individual age determinations depend rather strongly on the approach
taken to fitting their ages (cf. de Grijs et al., 2005). This, combined with a
strong dependence on the adopted reddening and metallicity, results in
individual age estimates of intermediate-age clusters associated with large
uncertainties.

Cluster ages can also be derived by comparing observed with model spectra.
Cross-identification of Beasley et al. (2004), Puzia et al. (2005), and
Caldwell et al. (2009) with the sample in this paper reveals that only six GCs
(and GC candidates) overlap with Puzia et al. (2005) (B006, B012, B045, and
B232) and Caldwell et al. (2009) (B049 and B195). The age deerminations of two
of these (B012 and B232) are inconsistent between Puzia et al. (2005) and this
paper: $10.2\pm 2.9$ Gyr and $9.0\pm 3.3$ Gyr obtained by Puzia et al. (2005)
compared to $2.0\pm 0.1$ Gyr and $2.0\pm 0.1$ Gyr, respectively, obtained in
this paper. The ages of the other GCs are consistent among the different
determinations.

In fact, the ages of GCs derived by different authors based on a range of
methods are not always consistent. For example, the ages of B292 and B327
derived by Beasley et al. (2004) and Puzia et al. (2005) are $2.748\pm 1.151$
Gyr and $0.080\pm 0.929$ Gyr (Beasley et al., 2004) compared to $9.2\pm 3.3$
Gyr and $5.4\pm 1.4$ Gyr (Puzia et al., 2005), respectively. On the other
hand, Caldwell et al. (2009) estimated the age of B327 at $0.050$ Gyr. In
addition, the ages of clusters derived in the same paper but based on
different line-index measurements are not always consistent either and may
indeed differ significantly (see the upper panels of Fig. 5 in Puzia et al.,
2005).

## Acknowledgments

We are indebted to the referee for thoughtful comments and insightful
suggestions that improved this paper greatly. This study has been supported by
the Chinese National Natural Science Foundation through grants 10873016,
10803007, 10473012, 10573020, 10633020, 10673012, and 10603006, and by
National Basic Research Program of China (973 Program), No. 2007CB815403.

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Table 1BATC filter parameters and observational statistics

Filter |  $\lambda_{\rm central}$ (Å) | FWHM (Å) | Na | Exp.b | rmsc
---|---|---|---|---|---
$c$ | 4210 | 320 | 3 | 01:00 | 0.015
$d$ | 4540 | 340 | 3 | 01:00 | 0.009
$e$ | 4925 | 390 | 3 | 01:00 | 0.015
$f$ | 5270 | 340 | 3 | 01:00 | 0.006
$g$ | 5795 | 310 | 3 | 01:00 | 0.003
$h$ | 6075 | 310 | 3 | 01:00 | 0.003
$i$ | 6656 | 480 | 3 | 01:00 | 0.003
$j$ | 7057 | 300 | 3 | 01:00 | 0.008
$k$ | 7546 | 330 | 3 | 01:00 | 0.004
$m$ | 8023 | 260 | 3 | 01:00 | 0.003
$n$ | 8480 | 180 | 6 | 02:00 | 0.004
$o$ | 9182 | 260 | 6 | 02:00 | 0.003
$p$ | 9739 | 270 | 6 | 02:00 | 0.009

a Number of exposures for each BATC filter

b Exposure time (in hr:min)

cZero-point error (in mag)

Table 2BATC intermediate-band photometry of our sample of 39 GCs and GC candidates in M31. Name | $c$ | $d$ | $e$ | $f$ | $g$ | $h$ | $i$ | $j$ | $k$ | $m$ | $n$ | $o$ | $p$
---|---|---|---|---|---|---|---|---|---|---|---|---|---
B004 | 17.71 | 17.49 | 17.22 | 17.06 | 16.72 | 16.61 | 16.44 | 16.34 | 16.21 | 16.03 | 16.09 | 15.91 | 16.01
| 0.130 | 0.012 | 0.008 | 0.009 | 0.009 | 0.008 | 0.008 | 0.009 | 0.010 | 0.009 | 0.021 | 0.010 | 0.024
B006 | 16.68 | 16.17 | 15.84 | 15.67 | 15.29 | 15.25 | 15.09 | 14.98 | 14.82 | 14.67 | 14.70 | 14.58 | 14.53
| 0.009 | 0.005 | 0.004 | 0.004 | 0.004 | 0.004 | 0.004 | 0.003 | 0.004 | 0.003 | 0.008 | 0.005 | 0.008
B008 | 17.83 | 17.33 | 17.04 | 16.88 | 16.51 | 16.43 | 16.26 | 16.14 | 16.01 | 15.87 | 15.73 | 15.80 | 15.73
| 0.016 | 0.010 | 0.007 | 0.008 | 0.008 | 0.007 | 0.008 | 0.008 | 0.009 | 0.007 | 0.015 | 0.011 | 0.019
B010 | 17.48 | 17.21 | 16.94 | 16.79 | 16.50 | 16.44 | 16.25 | 16.17 | 16.10 | 15.95 | 16.00 | 15.83 | 15.82
| 0.014 | 0.010 | 0.007 | 0.008 | 0.008 | 0.007 | 0.008 | 0.008 | 0.011 | 0.008 | 0.019 | 0.012 | 0.023
B012 | 15.90 | 15.58 | 15.34 | 15.20 | 14.91 | 14.85 | 14.71 | 14.63 | 14.55 | 14.40 | 14.45 | 14.36 | 14.35
| 0.006 | 0.004 | 0.003 | 0.003 | 0.003 | 0.003 | 0.003 | 0.003 | 0.004 | 0.003 | 0.007 | 0.004 | 0.007
B013 | 18.35 | 17.86 | 17.51 | 17.36 | 16.99 | 16.92 | 16.75 | 16.64 | 16.47 | 16.33 | 16.36 | 16.24 | 16.19
| 0.022 | 0.012 | 0.009 | 0.010 | 0.010 | 0.010 | 0.009 | 0.010 | 0.012 | 0.009 | 0.029 | 0.015 | 0.027
B016 | 18.64 | 18.08 | 17.78 | 17.62 | 17.24 | 17.15 | 16.95 | 16.82 | 16.68 | 16.51 | 16.56 | 16.33 | 16.33
| 0.027 | 0.016 | 0.011 | 0.012 | 0.012 | 0.011 | 0.011 | 0.010 | 0.014 | 0.010 | 0.028 | 0.016 | 0.029
B019 | 15.75 | 15.45 | 15.15 | 14.99 | 14.61 | 14.53 | 14.38 | 14.25 | 14.11 | 13.96 | 13.89 | 13.80 | 13.76
| 0.006 | 0.004 | 0.003 | 0.003 | 0.003 | 0.003 | 0.003 | 0.003 | 0.003 | 0.003 | 0.006 | 0.004 | 0.007
B020 | 15.61 | 15.29 | 15.06 | 14.92 | 14.54 | 14.48 | 14.36 | 14.24 | 14.12 | 13.95 | 13.99 | 13.92 | 13.85
| 0.006 | 0.003 | 0.003 | 0.003 | 0.003 | 0.003 | 0.003 | 0.003 | 0.003 | 0.003 | 0.006 | 0.004 | 0.007
B022 | 17.96 | 17.74 | 17.53 | 17.40 | 17.09 | 17.05 | 16.96 | 16.89 | 16.80 | 16.65 | 16.65 | 16.59 | 16.61
| 0.022 | 0.016 | 0.013 | 0.014 | 0.014 | 0.013 | 0.015 | 0.016 | 0.022 | 0.017 | 0.042 | 0.028 | 0.047
B026 | 18.58 | 18.09 | 17.70 | 17.55 | 17.15 | 17.06 | 16.88 | 16.72 | 16.54 | 16.37 | 16.27 | 16.18 | 16.19
| 0.031 | 0.023 | 0.016 | 0.018 | 0.020 | 0.015 | 0.017 | 0.015 | 0.018 | 0.018 | 0.033 | 0.022 | 0.035
B035 | 18.45 | 17.98 | 17.68 | 17.55 | 17.17 | 17.06 | 16.92 | 16.81 | 16.62 | 16.49 | 16.52 | 16.39 | 16.33
| 0.026 | 0.015 | 0.011 | 0.011 | 0.012 | 0.011 | 0.011 | 0.011 | 0.013 | 0.011 | 0.030 | 0.018 | 0.028
B045 | 16.88 | 16.41 | 16.08 | 15.94 | 15.55 | 15.48 | 15.30 | 15.19 | 15.06 | 14.92 | 14.93 | 14.77 | 14.75
| 0.010 | 0.006 | 0.004 | 0.005 | 0.005 | 0.004 | 0.004 | 0.004 | 0.005 | 0.004 | 0.009 | 0.007 | 0.010
B047 | 18.36 | 17.95 | 17.68 | 17.59 | 17.23 | 17.15 | 17.02 | 16.96 | 16.86 | 16.69 | 16.77 | 16.70 | 16.73
| 0.025 | 0.015 | 0.011 | 0.011 | 0.013 | 0.011 | 0.012 | 0.012 | 0.016 | 0.015 | 0.038 | 0.023 | 0.035
B049 | 17.93 | 17.76 | 17.70 | 17.61 | 17.43 | 17.42 | 17.30 | 17.25 | 17.16 | 17.12 | 17.28 | 16.92 | 17.92
| 0.025 | 0.022 | 0.020 | 0.021 | 0.024 | 0.019 | 0.021 | 0.024 | 0.026 | 0.021 | 0.061 | 0.040 | 0.412
B050 | 17.68 | 17.32 | 17.03 | 16.87 | 16.49 | 16.42 | 16.27 | 16.14 | 16.01 | 15.84 | 15.78 | 15.70 | 15.73
| 0.020 | 0.014 | 0.011 | 0.010 | 0.012 | 0.010 | 0.011 | 0.011 | 0.013 | 0.012 | 0.026 | 0.017 | 0.028
B052 | 19.02 | 18.24 | 17.64 | 17.27 | 16.92 | 16.76 | 16.53 | 16.38 | 16.23 | 16.04 | 15.89 | 15.73 | 15.65
| 0.046 | 0.020 | 0.012 | 0.011 | 0.012 | 0.010 | 0.009 | 0.009 | 0.012 | 0.009 | 0.020 | 0.013 | 0.021
B062 | 18.86 | 18.17 | 17.66 | 17.24 | 16.96 | 16.74 | 16.52 | 16.44 | 16.31 | 16.13 | 15.98 | 15.83 | 15.79
| 0.042 | 0.021 | 0.014 | 0.010 | 0.013 | 0.010 | 0.011 | 0.011 | 0.014 | 0.011 | 0.026 | 0.016 | 0.024
B074 | 17.55 | 17.16 | 16.91 | 16.80 | 16.43 | 16.35 | 16.22 | 16.14 | 16.03 | 15.89 | 15.92 | 15.84 | 15.80
| 0.014 | 0.010 | 0.007 | 0.007 | 0.008 | 0.007 | 0.008 | 0.008 | 0.009 | 0.008 | 0.027 | 0.013 | 0.020
B081 | 17.05 | 17.01 | 16.87 | 16.81 | 16.59 | 16.42 | 16.44 | 16.18 | 16.08 | 16.01 | 15.95 | 15.53 | 15.86
| 0.016 | 0.015 | 0.013 | 0.013 | 0.015 | 0.014 | 0.024 | 0.034 | 0.032 | 0.029 | 0.040 | 0.049 | 0.107
B089 | 18.24 | 18.22 | 18.16 | 18.16 | 18.11 | 18.16 | 18.16 | 18.16 | 18.07 | 18.01 | 18.49 | 18.17 | 18.34
| 0.027 | 0.026 | 0.026 | 0.024 | 0.039 | 0.034 | 0.041 | 0.045 | 0.050 | 0.047 | 0.126 | 0.090 | 0.163
Table 2Continued. Name | $c$ | $d$ | $e$ | $f$ | $g$ | $h$ | $i$ | $j$ | $k$ | $m$ | $n$ | $o$ | $p$
---|---|---|---|---|---|---|---|---|---|---|---|---|---
B100 | 18.82 | 18.31 | 18.04 | 17.92 | 17.63 | 17.61 | 17.31 | 17.25 | 17.24 | 17.21 | 17.24 | 16.95 | 16.91
| 0.050 | 0.030 | 0.026 | 0.026 | 0.027 | 0.025 | 0.026 | 0.048 | 0.031 | 0.033 | 0.065 | 0.037 | 0.170
B129 | … | … | 18.41 | 17.71 | 16.83 | 16.59 | 16.07 | 15.79 | 15.47 | 15.21 | 14.99 | 14.71 | 14.62
| … | … | 0.090 | 0.059 | 0.034 | 0.030 | 0.022 | 0.019 | 0.016 | 0.014 | 0.014 | 0.012 | 0.014
B156 | 17.67 | 17.32 | 17.09 | 16.82 | 16.53 | 16.64 | 16.44 | 16.35 | 16.17 | 16.20 | 16.18 | 16.13 | 16.40
| 0.018 | 0.011 | 0.008 | 0.008 | 0.008 | 0.010 | 0.012 | 0.014 | 0.012 | 0.031 | 0.021 | 0.035 | 0.008
B168 | 19.50 | 18.76 | 18.23 | 17.96 | 17.29 | 17.13 | 16.78 | 16.60 | 16.28 | 16.07 | 15.95 | 15.80 | 15.69
| 0.083 | 0.053 | 0.030 | 0.026 | 0.025 | 0.017 | 0.015 | 0.015 | 0.014 | 0.010 | 0.027 | 0.013 | 0.020
B170 | 18.27 | 17.90 | 17.61 | 17.46 | 17.11 | 17.06 | 16.84 | 16.76 | 16.66 | 16.52 | 16.46 | 16.38 | 16.44
| 0.025 | 0.020 | 0.012 | 0.013 | 0.014 | 0.012 | 0.012 | 0.014 | 0.015 | 0.014 | 0.033 | 0.018 | 0.141
B195 | 18.97 | 18.78 | 18.61 | 18.57 | 18.38 | 18.36 | 18.35 | 18.11 | 18.20 | 18.04 | 17.96 | 17.96 | …
| 0.046 | 0.035 | 0.028 | 0.035 | 0.044 | 0.033 | 0.044 | 0.044 | 0.062 | 0.059 | 0.109 | 0.074 | …
B199 | 18.27 | 18.00 | 17.80 | 17.62 | 17.44 | 17.41 | 17.22 | 17.10 | 17.06 | 17.00 | 17.05 | 16.87 | 17.06
| 0.024 | 0.018 | 0.012 | 0.013 | 0.016 | 0.013 | 0.014 | 0.016 | 0.018 | 0.017 | 0.039 | 0.022 | 0.060
B207 | 18.04 | 17.74 | 17.53 | 17.36 | 17.14 | 17.10 | 16.93 | 16.84 | 16.81 | 16.73 | 16.71 | 16.59 | 16.64
| 0.020 | 0.014 | 0.011 | 0.012 | 0.014 | 0.013 | 0.014 | 0.015 | 0.020 | 0.015 | 0.039 | 0.023 | 0.053
B212 | 16.17 | 15.91 | 15.69 | 15.51 | 15.31 | 15.28 | 15.10 | 15.01 | 14.96 | 14.91 | 14.84 | 14.76 | 14.80
| 0.007 | 0.005 | 0.004 | 0.004 | 0.004 | 0.004 | 0.004 | 0.004 | 0.005 | 0.004 | 0.011 | 0.006 | 0.012
B219 | 17.25 | 16.90 | 16.63 | 16.44 | 16.15 | 16.05 | 15.88 | 15.76 | 15.62 | 15.46 | 15.46 | 15.32 | 15.33
| 0.013 | 0.008 | 0.006 | 0.006 | 0.007 | 0.006 | 0.006 | 0.006 | 0.007 | 0.006 | 0.014 | 0.008 | 0.018
B226 | 19.13 | 18.51 | 18.10 | 17.77 | 17.55 | 17.43 | 17.15 | 17.05 | 16.97 | 16.82 | 16.63 | 16.56 | 16.49
| 0.044 | 0.029 | 0.015 | 0.015 | 0.018 | 0.015 | 0.016 | 0.016 | 0.022 | 0.016 | 0.041 | 0.021 | 0.045
B230 | 16.44 | 16.33 | 16.13 | 15.98 | 15.75 | 15.68 | 15.56 | 15.47 | 15.41 | 15.21 | 15.21 | 15.20 | 15.20
| 0.009 | 0.006 | 0.005 | 0.005 | 0.006 | 0.005 | 0.005 | 0.006 | 0.007 | 0.005 | 0.015 | 0.008 | 0.020
B232 | 16.15 | 16.02 | 15.80 | 15.65 | 15.34 | 15.28 | 15.17 | 15.06 | 14.98 | 14.80 | 14.74 | 14.76 | 14.71
| 0.008 | 0.005 | 0.004 | 0.005 | 0.005 | 0.005 | 0.005 | 0.005 | 0.006 | 0.006 | 0.011 | 0.008 | 0.016
B233 | 16.41 | 16.19 | 15.94 | 15.81 | 15.44 | 15.38 | 15.26 | 15.15 | 15.01 | 14.85 | 14.85 | 14.73 | 14.90
| 0.010 | 0.008 | 0.007 | 0.006 | 0.007 | 0.006 | 0.007 | 0.006 | 0.008 | 0.007 | 0.010 | 0.015 | 0.019
B236 | 17.86 | 17.69 | 17.52 | 17.38 | 17.08 | 17.03 | 16.88 | 16.75 | 16.47 | 16.40 | 16.45 | 16.76 | 16.22
| 0.021 | 0.017 | 0.012 | 0.012 | 0.015 | 0.012 | 0.012 | 0.018 | 0.023 | 0.040 | 0.021 | 0.039 | 0.164
B237 | 17.92 | 17.70 | 17.45 | 17.31 | 17.01 | 16.94 | 16.79 | 16.70 | 16.63 | 16.48 | 16.50 | 16.42 | 16.47
| 0.020 | 0.015 | 0.012 | 0.012 | 0.015 | 0.013 | 0.015 | 0.015 | 0.016 | 0.018 | 0.033 | 0.024 | 0.145
B238 | 17.39 | 17.02 | 16.73 | 16.58 | 16.23 | 16.13 | 15.97 | 15.88 | 15.74 | 15.66 | 15.58 | 15.58 | 15.45
| 0.014 | 0.007 | 0.006 | 0.006 | 0.007 | 0.012 | 0.007 | 0.016 | 0.016 | 0.014 | 0.019 | 0.011 | 0.055
B239 | 17.88 | 17.79 | 17.51 | 17.43 | 17.01 | 16.90 | 16.77 | 16.66 | 16.52 | 16.43 | 16.33 | 16.32 | 16.15
| 0.156 | 0.062 | 0.040 | 0.037 | 0.033 | 0.025 | 0.017 | 0.032 | 0.032 | 0.026 | 0.037 | 0.063 | 0.103
Table 3GALEX, broad-band, and 2MASS photometry of the 39 M31 GCs and GC candidates. Name |  $c$††footnotemark:  | FUV | NUV | $U$ | $B$ | $V$ | $R$ | $I$ | $J$ | $H$ | $K_{s}$
---|---|---|---|---|---|---|---|---|---|---|---
B004 | 1 | … | 22.25 | 18.29 | 17.87 | 16.95 | 16.36 | 15.73 | 14.91 | 14.36 | 14.19
|  | … | 0.07 | 0.03 | 0.01 | 0.01 | 0.02 | 0.01 | 0.02 | 0.07 | 0.05
B006 | 1 | … | 21.41 | 16.94 | 16.49 | 15.53 | 14.97 | 14.31 | 13.48 | 12.75 | 12.61
|  | … | 0.04 | 0.02 | 0.01 | 0.01 | 0.01 | 0.01 | 0.03 | 0.03 | 0.03
B008 | 1 | … | 22.59 | 18.16 | 17.66 | 16.56 | 16.21 | 15.51 | 14.68 | 14.17 | 13.98
|  | … | 0.12 | 0.08 | 0.05 | 0.05 | 0.05 | 0.05 | 0.05 | 0.07 | 0.06
B010 | 1 | 21.93 | 20.87 | 17.65 | 17.50 | 16.66 | 16.12 | 15.48 | 14.76 | 14.41 | 14.07
|  | 0.08 | 0.03 | 0.02 | 0.01 | 0.01 | 0.01 | 0.01 | 0.03 | 0.07 | 0.06
B012 | 1 | 20.10 | 19.02 | 15.99 | 15.86 | 15.13 | 14.62 | 14.08 | 13.36 | 12.79 | 12.72
|  | 0.02 | 0.01 | 0.01 | 0.01 | 0.01 | 0.01 | 0.01 | 0.03 | 0.03 | 0.03
B013 | 1 | … | … | 18.56 | 18.06 | 17.19 | 16.60 | 15.96 | 15.18 | 14.61 | 14.34
|  | … | … | 0.05 | 0.02 | 0.01 | 0.02 | 0.02 | 0.03 | 0.07 | 0.05
B016 | 1 | … | … | 18.86 | 18.58 | 17.58 | 16.85 | 16.15 | 15.18 | 14.18 | 14.05
|  | … | … | 0.08 | 0.04 | 0.01 | 0.03 | 0.02 | 0.08 | 0.07 | 0.10
B019 | 1 | 20.81 | 19.97 | 16.36 | 15.94 | 14.93 | 14.31 | 13.74 | 12.86 | 12.10 | 11.96
|  | 0.04 | 0.02 | 0.01 | 0.01 | 0.01 | 0.05 | 0.01 | 0.02 | 0.03 | 0.02
B020 | 1 | 20.05 | 19.20 | 15.98 | 15.74 | 14.91 | 14.37 | 13.65 | 12.97 | 12.26 | 12.21
|  | 0.02 | 0.01 | 0.08 | 0.05 | 0.05 | 0.05 | 0.05 | 0.02 | 0.03 | 0.03
B022 | 1 | 22.69 | 21.20 | 18.14 | 18.09 | 17.36 | 16.97 | 16.35 | 15.75 | 15.04 | 15.48
|  | 0.16 | 0.04 | 0.08 | 0.02 | 0.01 | 0.02 | 0.02 | 0.08 | 0.10 | 0.12
B026 | 1 | … | … | 19.14 | 18.60 | 17.53 | 16.88 | 16.22 | 15.10 | 14.48 | 14.00
|  | … | … | 0.06 | 0.02 | 0.01 | 0.03 | 0.02 | 0.08 | 0.07 | 0.05
B035 | 1 | … | 22.61 | 18.52 | 18.37 | 17.48 | 16.81 | 16.24 | 15.30 | 14.67 | 14.42
|  | … | 0.10 | 0.08 | 0.03 | 0.01 | 0.02 | 0.02 | 0.08 | 0.07 | 0.10
B045 | 1 | … | 21.07 | 17.09 | 16.72 | 15.78 | 15.19 | 14.54 | 13.73 | 13.00 | 12.89
|  | … | 0.03 | 0.02 | 0.01 | 0.01 | 0.01 | 0.01 | 0.03 | 0.04 | 0.03
B047 | 1 | 22.68 | 21.30 | 18.32 | 18.23 | 17.51 | 16.88 | 16.30 | 15.86 | 15.24 | 15.47
|  | 0.15 | 0.04 | 0.06 | 0.02 | 0.01 | 0.03 | 0.02 | 0.08 | 0.10 | 0.12
B049 | 1 | … | 21.55 | 18.26 | 18.08 | 17.56 | 17.11 | 16.87 | 15.61 | 15.33 | 14.68
|  | … | 0.06 | 0.09 | 0.04 | 0.01 | 0.04 | 0.04 | 0.08 | 0.10 | 0.10
B050 | 1 | … | 22.18 | 18.09 | 17.76 | 16.84 | 16.27 | 15.66 | 14.72 | 14.22 | 13.96
|  | … | 0.09 | 0.05 | 0.02 | 0.01 | 0.02 | 0.01 | 0.03 | 0.07 | 0.05
B052 | 4 | … | … | 19.80 | 18.62 | 17.21 | 16.54 | 15.77 | 14.70 | 14.01 | 13.40
|  | … | … | 0.08 | 0.02 | 0.01 | 0.02 | 0.02 | 0.04 | 0.07 | 0.05
B062 | 4 | … | … | 19.33 | 18.58 | 17.24 | 16.61 | 15.82 | 14.89 | 14.21 | 13.66
|  | … | … | 0.08 | 0.02 | 0.01 | 0.02 | 0.01 | 0.04 | 0.07 | 0.05
B074 | 1 | 22.12 | 20.75 | 17.54 | 17.40 | 16.65 | 16.14 | 15.58 | 14.83 | 13.95 | 14.11
|  | 0.07 | 0.02 | 0.03 | 0.01 | 0.01 | 0.01 | 0.01 | 0.02 | 0.04 | 0.04
B081 | 1 | 21.73 | 20.47 | 17.60 | 17.34 | 16.80 | 16.36 | 15.73 | 14.82 | 14.01 | 13.96
|  | 0.13 | 0.04 | 0.02 | 0.01 | 0.01 | 0.02 | 0.02 | 0.03 | 0.07 | 0.05
B089 | 2 | 19.89 | 19.62 | 17.96 | 18.28 | 18.18 | 18.22 | 17.70 | … | … | …
|  | 0.03 | 0.02 | 0.05 | 0.04 | 0.03 | 0.06 | 0.06 | … | … | …
Table 3Continued.

Name | $c$ | FUV | NUV | $U$ | $B$ | $V$ | $R$ | $I$ | $J$ | $H$ | $K_{s}$
---|---|---|---|---|---|---|---|---|---|---|---
B100 | 1 | 22.37 | … | 18.94 | 19.05 | 17.91 | … | 17.77 | 15.85 | 14.70 | 14.67
|  | 0.19 | … | 0.08 | 0.07 | 0.05 | … | 0.07 | 0.08 | 0.07 | 0.10
B129 | 1 | … | … | … | 19.56 | 17.40 | … | 14.69 | 13.25 | 12.40 | 12.19
|  | … | … | … | 0.05 | 0.05 | … | 0.05 | 0.03 | 0.03 | 0.04
B156 | 1 | … | 20.99 | 17.89 | 17.63 | 16.84 | 16.37 | 15.87 | … | … | …
|  | … | 0.09 | 0.02 | 0.02 | 0.01 | 0.02 | 0.05 | … | … | …
B168 | 1 | … | … | 20.82 | 19.23 | 17.63 | 16.69 | 15.72 | 14.52 | 13.43 | 13.37
|  | … | … | 0.08 | 0.06 | 0.01 | 0.03 | 0.02 | 0.06 | 0.04 | 0.08
B170 | 1 | … | … | 18.90 | 18.37 | 17.39 | 16.80 | 16.17 | 15.38 | 14.75 | 14.61
|  | … | … | 0.06 | 0.02 | 0.01 | 0.02 | 0.02 | 0.08 | 0.07 | 0.10
B195 | 2 | … | … | 19.94 | 18.97 | 18.57 | 18.02 | 17.59 | … | … | …
|  | … | … | 0.08 | 0.06 | 0.01 | 0.07 | 0.05 | … | … | …
B199 | 1 | … | 21.53 | 18.45 | 18.37 | 17.60 | 17.03 | 16.57 | 16.06 | 15.42 | 15.39
|  | … | 0.10 | 0.08 | 0.03 | 0.01 | 0.03 | 0.02 | 0.10 | 0.10 | 0.12
B207 | 1 | 21.64 | 21.04 | 18.26 | 18.07 | 17.33 | 16.81 | 16.33 | 15.67 | 14.42 | 14.78
|  | 0.11 | 0.06 | 0.03 | 0.02 | 0.01 | 0.02 | 0.02 | 0.05 | 0.07 | 0.08
B212 | 1 | 20.27 | 19.16 | 16.23 | 16.22 | 15.48 | 15.00 | 14.48 | 13.82 | 13.17 | 13.11
|  | 0.05 | 0.02 | 0.02 | 0.01 | 0.01 | 0.01 | 0.01 | 0.03 | 0.04 | 0.05
B219 | 1 | … | 21.59 | 17.74 | 17.32 | 16.39 | 15.82 | 15.19 | 14.32 | 13.71 | 13.51
|  | … | 0.10 | 0.08 | 0.05 | 0.05 | 0.05 | 0.05 | 0.02 | 0.04 | 0.04
B226 | 2 | 22.09 | 21.61 | 19.08 | 19.04 | 17.65 | … | 16.32 | 15.21 | 14.47 | 14.14
|  | 0.14 | 0.09 | 0.08 | 0.05 | 0.05 | … | 0.05 | 0.08 | 0.07 | 0.10
B230 | 1 | 20.69 | 19.46 | 16.78 | 16.77 | 16.05 | 15.61 | 15.13 | 14.43 | 13.92 | 13.85
|  | 0.08 | 0.03 | 0.02 | 0.01 | 0.01 | 0.01 | 0.01 | 0.02 | 0.04 | 0.05
B232 | 1 | 20.67 | 19.49 | 16.53 | 16.38 | 15.70 | 15.20 | 14.65 | 13.94 | 13.36 | 13.25
|  | 0.06 | 0.02 | 0.01 | 0.01 | 0.01 | 0.01 | 0.01 | 0.03 | 0.04 | 0.05
B233 | 1 | 21.27 | 20.04 | 16.82 | 16.61 | 15.80 | 15.27 | 14.76 | 13.90 | 13.32 | 13.21
|  | 0.05 | 0.01 | 0.01 | 0.01 | 0.01 | 0.01 | 0.01 | 0.02 | 0.04 | 0.03
B236 | 1 | … | 21.07 | 18.21 | 18.20 | 17.38 | 16.97 | 16.24 | … | … | …
|  | … | 0.07 | 0.08 | 0.02 | 0.01 | 0.02 | 0.02 | … | … | …
B237 | 1 | … | 21.25 | 18.03 | 17.87 | 17.10 | 16.57 | 16.05 | 15.47 | 15.06 | 14.91
|  | … | 0.05 | 0.02 | 0.02 | 0.01 | 0.02 | 0.02 | 0.04 | 0.10 | 0.09
B238 | 1 | … | 21.91 | 17.73 | 17.39 | 16.42 | 15.86 | 15.22 | 14.46 | 13.72 | 13.67
|  | … | 0.08 | 0.02 | 0.01 | 0.01 | 0.01 | 0.01 | 0.04 | 0.04 | 0.05
B239 | 1 | … | … | 18.49 | 18.10 | 17.08 | 16.65 | 16.09 | 15.31 | 14.55 | 14.55
|  | … | … | 0.04 | 0.02 | 0.01 | 0.02 | 0.02 | 0.04 | 0.07 | 0.08

${\dagger}$ New classification flag, following RBC V3.5 notation. 1 =
confirmed GC, 2 = GC candidate, 4 = confirmed galaxy

Table 4Reddening values and metallicities for our 39 M31 GCs and GC
candidates.

Name | $E(B-V)$ | ref.a | $\rm[Fe/H]$ | ref.b
---|---|---|---|---
B004 | 0.07$\pm$ 0.02 | 1 |  $-0.31\pm$ 0.74 | 1
B006 | 0.09$\pm$ 0.02 | 1 |  $-0.58\pm$ 0.10 | 1
B008 | 0.21 | 2 |  $-0.41\pm$ 0.38 | 1
B010 | 0.22$\pm$ 0.01 | 1 |  $-1.77\pm$ 0.14 | 1
B012 | 0.12$\pm$ 0.01 | 1 |  $-1.65\pm$ 0.19 | 1
B013 | 0.13$\pm$ 0.02 | 1 |  $-1.01\pm$ 0.49 | 1
B016 | 0.30$\pm$ 0.02 | 1 |  $-0.78\pm$ 0.19 | 1
B019 | 0.20$\pm$ 0.01 | 1 |  $-1.09\pm$ 0.02 | 1
B020 | 0.12$\pm$ 0.01 | 1 |  $-1.07\pm$ 0.10 | 3
B022 | 0.04$\pm$ 0.03 | 1 |  $-1.64\pm$ 0.07 | 4
B026 | 0.15$\pm$ 0.02 | 1 |  $0.01\pm$ 0.38 | 1
B035 | 0.27$\pm$ 0.05 | 2 |  $-0.20\pm$ 0.54 | 1
B045 | 0.18$\pm$ 0.01 | 1 |  $-1.05\pm$ 0.25 | 1
B047 | 0.09$\pm$ 0.02 | 1 |  $-1.62\pm$ 0.41 | 1
B049 | 0.16$\pm$ 0.02 | 1 |  $-2.14\pm$ 0.55 | 1
B050 | 0.24$\pm$ 0.01 | 1 |  $-1.42\pm$ 0.37 | 1
B052 | 0.23$\pm$ 0.04 | 1 |  $0.12\pm$ 0.17 | 4
B062 | 0.26$\pm$ 0.03 | 1 |  $-0.47\pm$ 0.11 | 4
B074 | 0.19$\pm$ 0.01 | 1 |  $-1.88\pm$ 0.06 | 1
B081 | 0.11$\pm$ 0.02 | 1 |  $-1.74\pm$ 0.40 | 1
B089 | … | … | … | …
B100 | 0.48$\pm$ 0.08 | 1 |  $-2.21\pm$ 0.10 | 4
B129 | 1.16$\pm$ 0.06 | 1 |  $-1.21\pm$ 0.32 | 1
B156 | 0.10$\pm$ 0.02 | 1 |  $-1.51\pm$ 0.38 | 1
B168 | 0.54$\pm$ 0.05 | 1 |  $-0.12\pm$ 0.21 | 4
B170 | 0.10$\pm$ 0.02 | 1 |  $-0.54\pm$ 0.24 | 1
B195 | 0.12$\pm$ 0.00 | 1 |  $-1.48\pm$ 0.63 | 4
B199 | 0.10$\pm$ 0.02 | 1 |  $-1.59\pm$ 0.11 | 1
B207 | 0.05$\pm$ 0.02 | 2 |  $-0.81\pm$ 0.59 | 1
B212 | 0.13$\pm$ 0.01 | 1 |  $-1.75\pm$ 0.13 | 3
B219 | 0.05$\pm$ 0.03 | 1 |  $-0.01\pm$ 0.57 | 1
B226 | 1.08$\pm$ 0.06 | 1 | … | …
B230 | 0.15$\pm$ 0.01 | 1 |  $-2.17\pm$ 0.16 | 1
B232 | 0.14$\pm$ 0.01 | 1 |  $-1.83\pm$ 0.14 | 1
B233 | 0.17$\pm$ 0.01 | 1 |  $-1.59\pm$ 0.32 | 3
B236 | 0.07$\pm$ 0.05 | 1 |  $-1.01\pm$ 0.17 | 4
B237 | 0.14$\pm$ 0.02 | 1 |  $-2.09\pm$ 0.28 | 1
B238 | 0.11$\pm$ 0.02 | 1 |  $-0.57\pm$ 0.66 | 1
B239 | 0.09$\pm$ 0.01 | 1 |  $-1.18\pm$ 0.61 | 2

aThe reddening values are taken from Fan et al. (2008) (ref.=1) and Barmby et
al. (2000) (ref.=2).

bThe metallicities are taken from Perrett et al. (2002) (ref.=1), Barmby et
al. (2000) (ref.=2), Huchra et al. (1991) (ref.=3), and Fan et al. (2008)
(ref.=4).

Table 5Ages estimates for 35 GCs and GC candidates in M31. Name | Age | $\chi_{\rm min}^{2}$ | Name | Age | $\chi_{\rm min}^{2}$
---|---|---|---|---|---
| (Gyr) | (per degree of freedom) |  | (Gyr) | (per degree of freedom)
B004 | $4.10\pm 0.55$ | 3.13 | B100 | $0.50\pm 0.10$ | 14.38
B006 | $12.50\pm 0.65$ | 1.39 | B129 | $15.10\pm 0.70$ | 9.00
B008 | $2.00\pm 0.10$ | 6.54 | B156 | $4.90\pm 0.65$ | 2.09
B010 | $1.80\pm 0.10$ | 1.08 | B168 | $12.60\pm 0.20$ | 3.27
B012 | $2.00\pm 0.10$ | 1.54 | B170 | $4.00\pm 0.45$ | 1.39
B013 | $12.00\pm 2.00$ | 0.96 | B195 | $0.70\pm 0.15$ | 0.82
B016 | $2.40\pm 0.30$ | 1.95 | B199 | $3.30\pm 0.55$ | 1.38
B019 | $2.10\pm 0.10$ | 12.01 | B207 | $1.20\pm 0.10$ | 7.99
B020 | $1.80\pm 0.10$ | 7.50 | B212 | $1.80\pm 0.10$ | 0.75
B022 | $3.40\pm 0.15$ | 4.11 | B219 | $2.50\pm 0.15$ | 3.06
B026 | $3.50\pm 0.25$ | 3.28 | B230 | $1.60\pm 0.10$ | 4.59
B035 | $1.00\pm 0.10$ | 3.97 | B232 | $2.00\pm 0.10$ | 2.62
B045 | $8.80\pm 1.45$ | 0.78 | B233 | $2.30\pm 0.10$ | 3.73
B047 | $2.80\pm 0.20$ | 4.22 | B236 | $2.00\pm 0.25$ | 2.63
B049 | $1.60\pm 0.10$ | 7.82 | B237 | $3.50\pm 0.35$ | 1.41
B050 | $16.00\pm 0.30$ | 2.12 | B238 | $5.00\pm 0.45$ | 2.01
B074 | $2.10\pm 0.15$ | 2.12 | B239 | $14.50\pm 2.05$ | 1.70
B081 | $2.10\pm 0.20$ | 7.82 |  |  |