J/ApJ/708/817 RR Lyrae variables in M32 and M31 (Fiorentino+, 2010)
RR Lyrae variables in M32 and the disk of M31.
Fiorentino G., Monachesi A., Trager S.C., Lauer T.R., Saha A.,
Mighell K.J., Freedman W., Dressler A., Grillmair C., Tolstoy E.
<Astrophys. J., 708, 817-833 (2010)>
=2010ApJ...708..817F 2010ApJ...708..817F
ADC_Keywords: Photometry, HST ; Stars, variable ; Stars, population II ;
Galaxies, nearby
Keywords: galaxies: elliptical and lenticular, cD - stars: Population II -
galaxies: individual (M32, M31) - Local Group -
stars: variables: other
Abstract:
We observed two fields near M32 with the Advanced Camera for
Surveys/High Resolution Channel (ACS/HRC) on board the Hubble Space
Telescope. The main field, F1, is 1.8' from the center of M32; the
second field, F2, constrains the M31 background, and is 5.4' distant.
Each field was observed for 16 orbits in each of the F435W (narrow B)
and F555W (narrow V) filters. The duration of the observations allowed
RR Lyrae stars to be detected. A population of RR Lyrae stars
determined to belong to M32 would prove the existence of an ancient
population in that galaxy, a subject of some debate. We detected 17 RR
Lyrae variables in F1 and 14 in F2. A 1σ upper limit of 6 RR
Lyrae variables belonging to M32 is inferred from these two fields
alone. Use of our two ACS/WFC parallel fields provides better
constraints on the M31 background, however, and implies that 7+4-3
(68% confidence interval) RR Lyrae variables in F1 belong to M32. We
have therefore found evidence for an ancient population in M32. It
seems to be nearly indistinguishable from the ancient population of
M31. The RR Lyrae stars in the F1 and F2 fields have indistinguishable
mean V-band magnitudes, mean periods, distributions in the Bailey
diagram, and ratios of RRc to RRtotal types. However, the color
distributions in the two fields are different, with a population of
red RRab variables in F1 not seen in F2. We suggest that these might
be identified with the detected M32 RR Lyrae population, but the small
number of stars rules out a definitive claim.
Description:
We obtained deep B- (2005 Sep 20-22 and 2006 Feb 6-8) and V-band (2005
Sep 22-24 and 2006 Feb 9-12) imaging of two fields (F1 and F2) near
M32 using the ACS/HRC instrument on board HST during Cycle 14 (Program
GO-10572, PI: Lauer).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 96 17 F1 RR Lyrae properties
table3.dat 96 14 F2 RR Lyrae properties
table4.dat 72 992 Time-series magnitudes for RR Lyrae variables
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See also:
J/AJ/138/184 : RR Lyrae variables in 2 fields in M31 spheroid (Sarajedini+,
2009)
J/ApJS/182/216 : Surface photometry of Virgo ellipticals (Kormendy+, 2009)
J/ApJ/532/308 : Hot Horizontal Branch Stars in the Core of M32 (Brown+ 2000)
J/ApJ/504/113 : F175W and F275W photometry of M31 and M32 (Brown+, 1998)
J/AJ/104/1349 : Infrared-luminous giants in M32 (Freedman, 1992)
Byte-by-byte Description of file: table2.dat table3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Star number (<[FMT2010] F1 NN> in table 2 or
<[FMT2010] F2 NN> in table 3 in Simbad)
4- 5 I2 h RAh Hour of right ascension (J2000)
7- 8 I2 min RAm Minute of right ascension (J2000)
10- 15 F6.3 s RAs Second of right ascension (J2000)
17 A1 --- DE- Sign of declination (J2000)
18- 19 I2 deg DEd Degree of declination (J2000)
21- 22 I2 arcmin DEm Arcminute of declination (J2000)
24- 28 F5.2 arcsec DEs Arcsecond of declination (J2000)
30- 34 F5.3 d Per Period
36 I1 --- H [1/4] Order of the Fourier series used to
obtain the best fit
38- 48 F11.3 d Epoch Julian date where each curve shows its maximum
of light at phase φ=1
50- 54 F5.2 mag F435W HST/ACS F435W magnitude (B-band)
56- 60 F5.2 mag F555W HST/ACS F555W magnitude (V-band)
62- 66 F5.2 mag <Vmag> Mean V-band magnitude
68- 71 F4.2 mag B-V - color index
73- 76 F4.2 mag AB Extinction in B-band
78- 81 F4.2 mag AV Extinction in V-band
83- 86 F4.2 mag resB RMS deviation of the data points from the
fitting model, in B-band
88- 91 F4.2 mag resV RMS deviation of the data points from the
fitting model, in V-band
93- 96 A4 --- Type [RRc /RRab] RR-Lyrae type (RRc or RRab)
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Fld [F1/F2] F1 or F2 field (1)
4- 11 A8 --- --- [variable]
13- 14 I2 --- Seq Variable identification (<[FMT2010] F1 NN> or
<[FMT2010] F2 NN> in Simbad)
16- 26 F11.3 d JD-B Julian Date of F435W observation
28- 32 F5.2 mag F435W HST/ACS F435W filter VEGAMAG magnitude
34- 37 F4.2 mag e_F435W Photometric uncertainty in F435W
39- 43 F5.2 mag Bmag Equivalent Johnson-Cousins B band magnitude
45- 55 F11.3 d JD-V Julian Date of F555W observation
57- 61 F5.2 mag F555W HST/ACS F555W filter VEGAMAG magnitude
63- 66 F4.2 mag e_F555W Photometric uncertainty in F555W
68- 72 F5.2 mag Vmag Equivalent Johnson-Cousins V band magnitude
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Note (1): Log of observations for the two fields:
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Field RA (J2000) DE (J2000) Filt Exposure time Date
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F1 00 42 47.63 +40 50 27.4 F435W 16x1279+16x1320 2005/09/20-22
F1 00 42 47.63 +40 50 27.4 F555W 16x1279+16x1320 2005/09/22-24
F2 00 43 07.89 +40 54 14.5 F435W 16x1279+16x1320 2006/02/06-08
F2 00 43 07.89 +40 54 14.5 F555W 16x1279+16x1320 2006/02/09-12
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 13-Feb-2012