J/ApJ/756/108 HST VI photometry of variable stars in Leo T (Clementini+, 2012)
Variability and star formation in Leo T, the lowest luminosity star-forming
galaxy known today.
Clementini G., Cignoni M., Contreras Ramos R., Federici L., Ripepi V.,
Marconi M., Tosi M., Musella I.
<Astrophys. J., 756, 108 (2012)>
=2012ApJ...756..108C 2012ApJ...756..108C
ADC_Keywords: Stars, variable ; Photometry, HST ; Galaxies, nearby
Keywords: galaxies: dwarf; galaxies: individual: Leo T;
galaxies: stellar content; stars: formation;
stars: variables: Cepheids; stars: variables: RR Lyrae
Abstract:
We present results from the first combined study of variable stars and
star formation history (SFH) of the Milky Way "ultra-faint" dwarf
(UFD) galaxy Leo T, based on F606W and F814W multi-epoch archive
observations obtained with the Wide Field Planetary Camera 2 on board
the Hubble Space Telescope. We have detected 14 variable stars in the
galaxy. They include one fundamental-mode RR Lyrae star and 11
Anomalous Cepheids with periods shorter than 1 day, thus suggesting
the occurrence of multiple star formation episodes in this UFD, of
which one about 10 Gyr ago produced the RR Lyrae star. A new estimate
of the distance to Leo T of 409+29-27kpc (distance modulus of
23.06±0.15mag) was derived from the galaxy's RR Lyrae star. Our V,
V-I color-magnitude diagram (CMD) of Leo T reaches V∼29mag and shows
features typical of a galaxy in transition between dwarf irregular and
dwarf spheroidal types. A quantitative analysis of the SFH, based on
the comparison of the observed V, V-I CMD with the expected
distribution of stars for different evolutionary scenarios, confirms
that Leo T has a complex SFH dominated by two enhanced periods about
1.5 and 9 Gyr ago, respectively. The distribution of stars and gas
shows that the galaxy has a fairly asymmetric structure.
Description:
The multi-epoch images of Leo T (J2000=09:34:53.4=+17:03:05) used
in this paper were retrieved from the Hubble Space Telescope (HST)
archive. They were obtained with the Wide Field Planetary Camera 2
(WFPC2) from 2007 October 21 to December 9 as part of GO program 11084
(PI: D. Zucker), and consist of 16 F606W (V) and 26 F814W (I) frames,
each corresponding to a 1200s exposure.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 81 14 Identification and properties of the Leo T
variable stars
table3.dat 37 543 Johnson-Cousins V, I photometry of the
variable stars
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
J/A+A/562/A134 : A lower bound on the Milky Way mass (Bratek+, 2014)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJS/178/247 : Hα and [NII] survey in local 11 Mpc (Kennicutt+, 2008)
http://www.sdss.org/ : SDSS home page
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- Name Variable star identifier
(<[CCC2012] VNN> in Simbad)
5- 8 I04 --- ObjID [6438/7235]? SDSS last four numbers (1)
10- 11 I2 h RAh [9] SDSS hour of right ascension (J2000)
13- 14 I2 min RAm [34] SDSS minute of right ascension (J2000)
16- 20 F5.2 s RAs [50/59] SDSS second of right ascension (J2000)
22 A1 --- DE- [+] SDSS sign of declination (J2000)
23- 24 I2 deg DEd [17] SDSS degree of declination (J2000)
26- 27 I2 arcmin DEm [1/3] SDSS arcminute of declination (J2000)
29- 32 F4.1 arcsec DEs SDSS arcsecond of declination (J2000)
34 A1 --- fp [c] position read from HLA (2)
36- 39 A4 --- Type Variable star type (G1)
41- 46 F6.4 d Per [0.3/0.9] Period
48- 55 F8.4 d HJD Epoch (max); JD-2454000
57- 61 F5.2 mag <Vmag> [22.4/23.6] Mean HST/WFPC2 V-band magnitude
62 A1 --- u_<Vmag> Uncertainty flag on <Vmag>
64- 68 F5.2 mag <Imag> [21.9/23.2] Mean HST/WFPC2 I-band magnitude
69 A1 --- u_<Imag> Uncertainty flag on <Imag>
71- 74 F4.2 mag Av [0.1/1.1] V-band extinction
75 A1 --- u_Av Uncertainty flag on Av
77- 80 F4.2 mag Ai [0.1/0.7] I-band extinction
81 A1 --- u_Ai Uncertainty flag on Ai
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Note (1): Last four digits of the SDSS identification number,
the complete number is obtained by adding 587742061055830000.
Note (2): positions are from the SDSS, except those flagged with 'c'
which are from the 11084_17 WFPC2 LEO T image in the HLA-STScI.
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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 A1 --- Filt Filter used in the observation (V or I)
3- 5 A3 --- Name Variable star identifier (VNN)
7- 10 A4 --- Type Varibale star type (G1)
12- 23 F12.6 d HJD Heliocentric Julian Date; (HJD-2400000)
25- 31 F7.4 mag mag [21.7/24] Observed magnitude in Filt
33- 37 F5.3 mag e_mag [0.01/0.1] Uncertainty in mag
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Global note:
Note (G1): Type as follows:
AC = Anomalous Cepheid
Bin? = Suspected binary
RRab = RR Lyrae star
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 25-Mar-2014