J/AJ/151/40 Differential BV photometry of 5 variables in M79 (Bond+, 2016)
A luminous yellow post-AGB star in the galactic globular cluster M79.
Bond H.E., Ciardullo R., Siegel M.H.
<Astron. J., 151, 40 (2016)>
=2016AJ....151...40B 2016AJ....151...40B (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, variable ; Photometry, UBV
Keywords: distance scale - globular clusters: individual: M79 -
stars: AGB and post-AGB - stars: evolution -
stars: variables: RR Lyrae
Abstract:
We report the discovery of a luminous F-type
post-asymptotic-giant-branch (PAGB) star in the Galactic globular
cluster (GC) M79 (NGC 1904). At visual apparent and absolute
magnitudes of V=12.20 and MV=-3.46, this "yellow" PAGB star is by a
small margin the visually brightest star known in any GC. It was
identified using CCD observations in the uBVI photometric system,
which is optimized to detect stars with large Balmer discontinuities,
indicative of very low surface gravities. Follow-up observations with
the SMARTS 1.3 and 1.5m telescopes show that the star is not variable
in light or radial velocity, and that its velocity is consistent with
cluster membership. Near- and mid-infrared observations with 2MASS and
WISE show no evidence for circumstellar dust. We argue that a sharp
upper limit to the luminosity function exists for yellow PAGB stars in
old populations, making them excellent candidates for Population II
standard candles, which are four magnitudes brighter than RR Lyrae
variables. Their luminosities are consistent with the stars being in a
PAGB evolutionary phase, with core masses of ∼0.53M☉. We also
detected four very hot stars lying above the horizontal branch
("AGB-manque" stars); along with the PAGB star, they are the brightest
objects in M79 in the near-ultraviolet. In the Appendix, we give
periods and light curves for five variables in M79: three RR Lyrae
stars, a Type II Cepheid, and a semiregular variable.
Description:
We have carried out a program of photometric monitoring of M79. The
observations, made by Chilean service personnel, used the 1.3m Small &
Moderate Aperture Research Telescope System (SMARTS) Consortium
telescope at Cerro Tololo Interamerican Observatory (CTIO) and its
ANDICAM CCD camera. Data were obtained on the M79
Post-Asymptotic-Giant-Branch (PAGB; RA=5:24:10.36, Dec=-24:29:20.6;
the PAGB star is also cataloged as TYC 6479-422-1 and 2MASS
J05241036-2429206) star and surrounding field on 224 nights between
2007 February 20 and 2011 May 8. On each night, two exposures of 30s
each were obtained in B and in V. The usable field of view of these
images is about 5.6'*5.6'. The data for the five variable stars are
included in Table5.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 47 5 M79 variables in our 1.3m monitoring field
table4.dat 27 5 Elements for M79-V6
table5.dat 23 4365 Differential photometry of variable stars in M79
--------------------------------------------------------------------------------
See also:
B/gcvs : General Catalogue of Variable Stars (Samus+ 2007-2013)
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
J/A+A/548/A92 : VrI light curves of NGC1904 variables (Kains+, 2012)
J/MNRAS/370/1979 : JHKs photometry of T2Cs in globular clusters
(Matsunaga+, 2006)
J/A+AS/144/5 : Nearby globular clusters photometric catalog
(Rosenberg+, 2000)
J/A+AS/125/1 : The globular cluster NGC 1904 (Kravtsov+ 1997)
J/AJ/107/230 : BVRI CCD photometry of NGC 1904 (Alcaino+, 1994)
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Star M79 variable star identifier
5- 8 A4 --- Type Star type
10- 17 F8.3 d T0 ? Heliocentric Julian Date at zero phase T0
(HJD-2450000)
19- 22 A4 --- f_T0 See Table 4 for seasonal elements
24- 32 F9.6 d Per ? Period
34- 37 A4 --- f_Per See Table 4 for seasonal elements
39- 47 A9 d IPer ? Period interval for V8
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 yr Year0 Starting year of season
5 A1 --- --- [-]
6- 9 I4 yr Year1 ? Ending year of season
11- 18 F8.3 d T0 Heliocentric Julian Date at zero phase T0
(HJD-2450000)
20- 27 F8.6 d Per Period
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Star M79 variable star identifier (V6, V7, V8, V13,
or V14)
5 A1 --- Band [BV] Band used in the observation (B or V)
7- 16 F10.5 d HJD Heliocentric Julian Date (HJD-2450000)
18- 23 F6.4 mag mag [0.6/5.17] Differential photometry in Band (1)
--------------------------------------------------------------------------------
Note (1): With respect to the sum of the intensities of eight comparison stars
in the 1.3-m field.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 12-Jul-2016