J/AJ/159/119 HST emission line survey of Andromeda. I. Be stars (Peters+, 2020)
The Hubble Space Telescope Advanced Camera for Surveys emission line survey of
Andromeda.
I. Classical Be stars.
Peters M., Wisniewski J.P., Williams B.F., Lomax J.R., Choi Y., Durbin M.,
Johnson L.C., Lewis A.R., Lutz J., Sigut T.A.A., Wallach A., Dalcanton J.J.
<Astron. J., 159, 119 (2020)>
=2020AJ....159..119P 2020AJ....159..119P
ADC_Keywords: Surveys; Stars, B-type; Stars, Be; Photometry, HST; Optical;
Spectral types
Keywords: Circumstellar disks ; Be stars ; Early-type stars ; H alpha photometry
Abstract:
We present results from a two epoch Hubble Space Telescope Hα
emission line survey of the Andromeda galaxy that overlaps the
footprint of the Panchromatic Hubble Andromeda Treasury (PHAT) survey.
We found 552 (542) classical Be stars and 8429 (8556) normal B-type
stars in epoch 1 (epoch 2), yielding an overall fractional Be content
of 6.15%±0.26% (5.96%±0.25%). The fractional Be content
decreased with spectral subtype from ∼23.6%±2.0% (∼23.9%±2.0%)
for B0-type stars to ∼3.1%±0.34% (∼3.4%±0.35%) for B8-type
stars in epoch 1 (epoch 2). We observed a clear population of cluster
Be stars at early fractional main-sequence lifetimes, indicating that
a subset of Be stars emerge onto the zero-age main sequence as rapid
rotators. Be stars are 2.8x rarer in M31 for the earliest subtypes
compared to the Small Magellanic Cloud, confirming that the fractional
Be content decreases in significantly more metal-rich environments
(like the Milky Way and M31). However, M31 does not follow a clear
trend of Be fraction decreasing with metallicity compared to the Milky
Way, which may reflect that the Be phenomenon is enhanced with
evolutionary age. The rate of disk-loss or disk-regeneration episodes
we observed, 22%±2%/yr, is similar to that observed for seven
other Galactic clusters reported in the literature, assuming these
latter transient fractions scale by a linear rate. The similar number
of disk-loss events (57) as disk-renewal events (43) was unexpected
since disk dissipation timescales can be ∼2x the typical timescales
for disk build-up phases.
Description:
We observed M31 with the Hubble Space Telescope (HST) in the 12 orbit
GO-13857 program (Dalcanton PI). Pure-parallel observations were made
with the Advanced Camera for Surveys/Wild Field Camera (ACS)/(WFC) and
WFC3/UVIS (UV-visible) camera at three distinct spatial locations that
coincided with regions of the galaxy previously observed via the
HST/PHAT (Panchromatic Hubble Andromeda Treasury;
Dalcanton+ 2012ApJS..200...18D 2012ApJS..200...18D) survey, yielding six distinct
pointings across M31.
We obtained a second epoch of observations of these same six pointings
approximately 1yr later (in 2015), when HST was able to achieve the
same view of these pure-parallel pointings.
Observations were made in both cameras using the F658N narrow-band
filters and using the F625W broadband filter.
A summary of our basic observational design is provided in Table1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 57 12 Summary of HST observations of M31 from GO-13857
table8.dat 179 18079 Source catalog
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/A+AS/134/489 : Be stars in MC young clusters (Keller+ 1999)
J/ApJ/622/1052 : byHα photometry of NGC 3766 (McSwain+, 2005)
J/ApJS/161/118 : byHα photometry in open clusters (McSwain+, 2005)
J/A+A/459/137 : Bright Be shell stars (Rivnius+, 2006)
J/ApJ/652/458 : BVRHα phot. of candidates Be stars (Wisniewski+,2006)
J/A+A/472/577 : NGC 330 Be stars and binaries (Martayan+, 2007)
J/A+A/462/683 : Velocities in SMC field of NGC 330 (Martayan+, 2007)
J/ApJ/700/1216 : Spectroscopy of Be stars in open clusters (McSwain+, 2009)
J/A+A/509/A11 : Hα emission-line objects SMC clusters (Martayan+,2010)
J/ApJ/709/1306 : Spectropolarimetry of 60 Cyg and π Aqr (Wisniewski+,2010)
J/ApJ/752/95 : PHAT stellar cluster survey. I. Year 1 (Johnson+, 2012)
J/A+A/553/A24 : Models for rotating stars (Georgy+, 2013)
J/ApJ/786/120 : Spectropolarimetric survey classical Be stars (Draper+,2014)
J/ApJ/792/121 : Photometric survey planetary nebulae in M31 (Veyette+, 2014)
J/ApJS/215/9 : PHAT X. UV-IR photometry of M31 stars (Williams+, 2014)
J/ApJ/802/127 : PHAT stellar cluster survey. II. AP catalog (Johnson+, 2015)
J/ApJ/827/33 : PHAT. XVI. Star cluster masses and ages (Johnson+, 2016)
J/AJ/153/252 : Photo. variability of BeSS-KELT stars (Labadie-Bartz+,2017)
J/MNRAS/465/4180 : Hα stars in M31 HST photometry (Prichard+, 2017)
J/A+A/610/A70 : 28 Cygni BRITE and SMEI satellite photometry (Baade+, 2018)
J/AJ/155/50 : WISE photo. of Be stars young open clusters (Granada+, 2018)
J/AJ/155/53 : Outbursts & disk variability Be stars (Labadie-Bartz+,2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1 I1 --- Epoch [1/2] Epoch number
3 I1 --- Pntg [1/6] Pointings
5- 8 I4 yr Obs.Y [2014/2015] Year of observation
10-12 A3 "month" Obs.M Month of observation
14-15 I2 d Obs.D Day of observation
17-23 A7 --- Inst Camera used ("WFC3" or "ACS/WFC")
25-26 I2 h RAh [0] Hour of right ascension (J2000)
28-29 I2 min RAm [44/45] Minute off right ascension (J2000)
31-35 F5.2 s RAs Second of right ascension (J2000)
37 A1 --- DE- [+] Sign of declination (J2000)
39-40 I2 deg DEd [41] Degree of declination (J2000)
42-43 I2 arcmin DEm [20/54] Arcminute of declination (J2000)
45-48 F4.1 arcsec DEs Arcsecond of declination (J2000)
50-52 I3 s Exp625 [750] Exposure time for F625W
54-57 I4 s Exp658 [3850] Exposurer time for F658N
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
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1- 1 I1 --- Pntg [4/6] Pointings
3- 3 I1 --- Epoch [1/2] Epoch
5- 11 I7 --- Index [35/2256863] Index
13- 30 F18.15 deg RAdeg [11.12/11.46] Right Ascension (J2000)
from Williams+ (2014, J/ApJS/215/9)
32- 49 F18.15 deg DEdeg [41.39/42] Declination (J2000)
from Williams+ (2014, J/ApJS/215/9)
51- 56 F6.3 mag F475W [20.3/26.8] HST/WFC3 F475W magnitude
from Williams+ (2014, J/ApJS/215/9)
58- 62 F5.3 mag e_F475W [0.002/0.2] 1σ uncertainty in F475W
64- 69 F6.3 mag F625W [20.2/25.6] HST/ACS-WFC F625W magnitude
from this work
71- 75 F5.3 mag e_F625W [0.004/0.1] 1σ uncertainty in F625W
77- 82 F6.3 mag F658N [20/24.7] HST/ACS-WFC F658N magnitude
from this work
84- 88 F5.3 mag e_F658N [0.008/0.2] 1σ uncertainty in F658N
90- 95 F6.3 mag F814W [20.2/25.8] HST/WFC3 F814W magnitude
from Williams+ (2014, J/ApJS/215/9)
97-101 F5.3 mag e_F814W [0.003/0.2] 1σ uncertainty in F814W
103-120 F18.16 [K] logTeff [4/4.6] Stellar effective surface temperature
122-139 F18.16 [cm/s2] logg50 [2.9/4.5] Surface gravity, 50th percentile
141-158 F18.16 [cm/s2] logg84 [3.7/4.5] Surface gravity, 84th percentile
160-163 I4 --- Cl [0/5933] Best estimate for cluster membership
(0=field star) (1)
165-169 A5 --- Be* Is the star a classical Be star?
171-173 A3 --- SpT Best estimate for the spectral type
based on logTeff
175-179 A5 --- Var* Exhibit variability between epochs (2)
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Note (1): The Cluster column indicates our best estimate for cluster membership,
with 0 denoting a field star and other numbers denoting the cluster ID
from Johnson+ (2015, J/ApJ/802/127 ; <[JSD2015] AP NNNNN> in Simbad).
Note (2): Variabilities as follows:
MAIN = denotes a star that maintained its disk between epochs;
LOST = denotes a star that experienced a disk-loss episode;
GAIN = denotes a star that experienced a disk-renewal episode;
BSTAR = denotes stars that were normal B-type stars in both epochs;
UNKWN = is a star that was detected in only one of the epochs.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 29-Apr-2020