J/ApJ/926/99 Above-horizontal-branch (AHB) stars in Gal. GCs (Davis+, 2022)
A census of above-horizontal-branch stars in Galactic globular clusters.
Davis B.D., Bond H.E., Siegel M.H., Ciardullo R.
<Astrophys. J., 926, 99 (2022)>
=2022ApJ...926...99D 2022ApJ...926...99D
ADC_Keywords: Clusters, globular; Stars, giant; Stars, horizontal branch;
Photometry, UBVRI; Proper motions; Magnitudes, absolute
Keywords: Globular star clusters ; Asymptotic giant branch stars ;
Post-asymptotic giant branch stars ; Horizontal branch stars
Abstract:
We have carried out a search for above-horizontal-branch (AHB)
stars-objects lying above the horizontal branch (HB) and blueward of
the asymptotic giant branch (AGB) in the color-magnitude diagram-in
97 Galactic and seven Magellanic Cloud globular clusters (GCs). We
selected AHB candidates based on photometry in the uBVI system, which
is optimized for detection of low-surface-gravity stars with large
Balmer jumps, in the color range -0.05≤(B-V)0≤1.0. We then used
Gaia astrometry and Gaussian-mixture modeling to confirm cluster
membership and remove field interlopers. Our final catalog contains
438 AHB stars, classified and interpreted in the context of post-HB
evolution as follows: (1) AHB1: 280 stars fainter than MV=-0.8,
evolving redward from the blue HB (BHB) toward the base of the AGB.
(2) Post-AGB (PAGB): 13 stars brighter than MV~-2.75, departing from
the top of the AGB and evolving rapidly blueward. (3) AHB2: 145 stars,
with absolute magnitudes between those of the AHB1 and PAGB groups.
This last category includes a mixture of objects leaving the extreme
BHB and evolving toward the AGB, and brighter ones moving back from
the AGB toward higher temperatures. Among the AHB1 stars are
59 RR Lyrae interlopers, observed by chance in our survey near maximum
light. PAGB and AHB2 stars (including W Virginis Cepheids)
overwhelmingly belong to GCs containing BHB stars, in accordance with
predictions of post-HB evolutionary tracks. We suggest that most W Vir
variables are evolving toward lower temperatures and are in their
first crossings of the instability strip. Nonvariable yellow PAGB
stars show promise as a Population II standard candle for distance
measurement.
Description:
The globular cluster (GC) uBVI observations discussed in this paper
were obtained by Bond H.E. with CCD cameras on the 0.9 and 1.5m
telescopes at Cerro Tololo Inter-American Observatory (CTIO), and the
0.9m and Mayall 4m telescopes at Kitt Peak National Observatory (KPNO)
between 1994 December and 2001 March, spread over 18 observing runs.
Table 11 presents an observing log detailing the observations of each
cluster.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
clusters.dat 8 109 List of observed globular clusters
(from Table 11); table added by CDS
table3.dat 176 438 The above-horizontal-branch (AHB) catalog;
for 64 globular clusters
table7.dat 52 21 Blue stars in M14 and M10 (see Section 7.4)
table11.dat 88 369 uBVI observations
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See also:
II/183 : UBVRI Photometric Standards (Landolt 1992)
VI/65 : Evolutionary models of evolved stars (Dorman+ 1993)
V/150 : Updated catalog of variable stars in globular clusters (Clement+ 2017)
J/ApJ/419/596 : Pop I UV radiation models (Dorman+, 1993)
J/ApJS/92/125 : Post-AGB evolution (Vassiliadis+, 1994)
J/A+A/299/755 : Stellar evolution. II. Post-AGB (Bloecker+, 1995)
J/AJ/112/601 : UV photometry in M79 (Hill+ 1996)
J/AJ/113/1026 : Fabry-Perot Observations of M15 (Gebhardt+ 1997)
J/A+A/360/472 : Proper motions in omega Centauri (van Leeuwen+, 2000)
J/AJ/121/318 : BV photometry in NGC 5986 (Alves+, 2001)
J/A+A/391/945 : HST phot. of 74 galactic globular clusters (Piotto+, 2002)
J/A+A/423/353 : Abundances of UV-bright stars (Jasniewicz+, 2004)
J/A+A/419/1123 : Equivalent widths of 3 post-AGB (Mooney+, 2004)
J/ApJ/628/729 : CCD BVIc photometry of M10 stars (Pollard+, 2005)
J/A+A/445/503 : Radial velocities in Omega Cen (NGC5139) (Reijns+, 2006)
J/MNRAS/382/1353 : Spectral atlas of omega Cen post-MS stars (van Loon+, 2007)
J/AcA/58/293 : Type-II and anomalous Cepheids in LMC (Soszynski+, 2008)
J/ApJS/193/1 : UBVRIJHK color-temperature calibration (Worthey+, 2011)
J/AJ/143/121 : UV data of Galactic globulars with GALEX (Schiavon+, 2012)
J/AJ/146/57 : NGC 6402. I. BV photometry (Contreras Pena+, 2013)
J/MNRAS/453/133 : WISE view of RV Tauri stars (Gezer+, 2015)
J/AJ/151/40 : Differential BV phot. of 5 variables in M79 (Bond+, 2016)
J/A+A/588/A25 : Post-AGB & CSPNe evol. models (Miller Bertolami, 2016)
J/A+A/589/A1 : Extreme HB stars in ω Cen (Randall+, 2016)
J/AJ/155/116 : Globular cluster M14. II. Variables (Contreras Pena+, 2018)
J/A+A/618/A15 : Parameters of EHB stars in ω Cen (Latour+, 2018)
J/A+A/622/A191 : 885 globular cluster giants abundances (Masseron+, 2019)
J/MNRAS/499/4026 : NGC 6254 variables VI light curves (Arellano Ferro+, 2020)
J/AJ/161/204 : Astrometry & phot. for 156 ZNG UV-bright stars (Bond+, 2021)
Byte-by-byte Description of file: clusters.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Cluster Globular cluster identifier
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Cluster Cluster identifier (NGC/IC number)
10- 13 A4 --- ClName Other cluster identifier
15- 20 I6 --- ID [52/350976] Star number
22- 30 F9.5 deg RAdeg Gaia EDR3 right Ascension (ICRS)
at Epoch=2016.0
32- 40 F9.5 deg DEdeg [-84/48] Gaia EDR3 declination (ICRS)
at Epoch=2016.0
42- 49 F8.5 mas/yr pmRA [-8.7/10.5] Gaia EDR3 proper motion in RA
51- 59 F9.5 mas/yr pmDE [-19.6/2.7] Gaia EDR3 proper motion in DE
61- 66 F6.1 arcsec Dist [1.5/1386] Distance from Cluster Center
68- 73 F6.3 mag VMag [-3.51/0.31] Absolute V band Vega magnitude (1)
75- 80 F6.3 mag (B-V)0 [-0.05/0.99] Intrinsic B-V color
82- 86 F5.3 mag (c2)0 [0.3/1.85] Intrinsic (u-B)-(B-V) color
88- 93 F6.3 mag umag [12.33/21.15] Apparent u band magnitude; Vega+1
95- 99 F5.3 mag e_umag [0.004/0.3] Uncertainty in umag
101-106 F6.3 mag Bmag [11/19.76] Apparent B band Vega magnitude
108-112 F5.3 mag e_Bmag [0.004/0.14] Uncertainty in Bmag
114-119 F6.3 mag Vmag [10.67/19.33] Apparent V band Vega magnitude
121-125 F5.3 mag e_Vmag [0.004/0.22] Uncertainty in Vmag
127-132 F6.3 mag Imag [9.94/18.8] Apparent I band Vega magnitude
134-138 F5.3 mag e_Imag [0.004/0.3] Uncertainty in Imag
140-145 F6.3 mas plx [-0.96/1.25] Gaia EDR3 parallax
147-151 F5.3 --- Mm [0.8/1] Membership Probability
153-157 A5 --- Type AHB Classification (2)
160-176 A17 --- PName Previous Identification(s) (3)
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Note (1): Absolute V magnitude based on distance modulus and reddening
given by Harris (2010arXiv1012.3224H 2010arXiv1012.3224H).
Note (2): Evolutionary classification scheme explained in text (Section 8.1)
and illustrated in Figure 16. Abbreviations as follows:
AHB1 = Fainter Above-Horizontal-Branch stars, likely evolving toward AGB;
280 occurrences
AHB2 = Brighter Above-Horizontal-Branch stars, uncertain evolutionary state;
145 occurrences
rPAGB = red post-AGB stars; 4 occurrences
yPAGB = yellow post-AGB stars; 9 occurrences.
Note (3): Abbreviations are:
V = variable star number from Clement+ 2001AJ....122.2587C 2001AJ....122.2587C (see V/150)
ZNG = From Zinn+ (1972A&A....18..390Z 1972A&A....18..390Z).
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- ClName M14 or M10
5- 12 A8 --- Cluster NGC number
14- 19 A6 --- ID Star identifier
21- 29 F9.5 deg RAdeg [254.2/264.5] Gaia EDR3 right ascension (ICRS)
at Epoch=2016.0
31- 38 F8.5 deg DEdeg [-4.2/-3.1] Gaia EDR3 declination (ICRS)
at Epoch=2016.0
40- 45 F6.3 mag (B-V)0 [-0.31/-0.046] (B-V) color index
47- 52 F6.3 mag VMag [-2.1/1.5] Absolute V magnitude
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Byte-by-byte Description of file: table11.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Type Globular cluster type (1)
6- 13 A8 --- Cluster Globular cluster identifier
15- 20 A6 --- ClName Other cluster identifier
22- 27 A6 --- Field Field within cluster (2)
29- 33 F5.2 mag DM [12.37/21.1] Distance modulus in V band (3)
35- 38 F4.2 mag E(B-V) [0/1.24] The (B-V) color excess (3)
40- 43 I4 yr Obs.Y [1994/2001] UT Year of the observation
45- 47 A3 "month" Obs.M UT Month of the observation
49- 50 I2 d Obs.D UT Day of the observation
52- 55 A4 --- Tel Telescope (4)
57- 64 A8 s Exp-u The u band exposure time
66- 72 A7 s Exp-B The B band exposure time
74- 80 A7 s Exp-V The V band exposure time
82- 88 A7 s Exp-I The I band exposure time
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Note (1): Cluster type as follows:
GGC = Galactic Globular Cluster (358 occurrences);
MCGC = Magellanic Cloud Old Globular Cluster (11 occurrences).
Note (2): CTR = pointing centered on cluster; if listed fields are NW, NE, SW,
and SE, this indicates a 2x2 mosaic; if N, S, W, and E are also
listed, this indicates a 3x3 mosaic. ROA 24 = pointing centered on
this yellow PAGB star in ω Cen.
Note (3): Taken from Harris (2010arXiv1012.3224H 2010arXiv1012.3224H) for Galactic clusters;
see text for sources for Magallanic Cloud clusters.
Note (4): Telescope as follows:
KP4 = KPNO Mayall 4-m (7 occurrences);
KP36 = KPNO 0.9-m (102 occurrences);
CT60 = CTIO 1.5-m (17 occurrences);
CT36 = CTIO 0.9-m (243 occurrences).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 27-Oct-2023