J/AJ/144/88 Spectroscopy of 6 LMC RR Lyrae and 3 SMC RR Lyrae (Haschke+, 2012)
Chemical abundances of metal-poor RR Lyrae stars in the Magellanic Clouds.
Haschke R., Grebel E.K., Frebel A., Duffau S., Hansen C.J., Koch A.
<Astron. J., 144, 88 (2012)>
=2012AJ....144...88H 2012AJ....144...88H
ADC_Keywords: Magellanic Clouds ; Stars, variable ; Equivalent widths ;
Abundances, [Fe/H] ; Radial velocities
Keywords: Magellanic Clouds - stars: abundances - stars: variables: RR Lyrae -
techniques: spectroscopic
Abstract:
We present for the first time a detailed spectroscopic study of
chemical element abundances of metal-poor RR Lyrae stars in the Large
and Small Magellanic Cloud (LMC and SMC). Using the MagE echelle
spectrograph at the 6.5m Magellan telescopes, we obtain medium
resolution (R∼2000-6000) spectra of six RR Lyrae stars in the LMC and
three RR Lyrae stars in the SMC. These stars were chosen because their
previously determined photometric metallicities were among the lowest
metallicities found for stars belonging to the old populations in the
Magellanic Clouds. We find the spectroscopic metallicities of these
stars to be as low as [Fe/H]spec=-2.7dex, the lowest metallicity yet
measured for any star in the Magellanic Clouds. We confirm that for
metal-poor stars, the photometric metallicities from the Fourier
decomposition of the light curves are systematically too high compared
to their spectroscopic counterparts. However, for even more metal-poor
stars below [Fe/H]phot←2.8dex this trend is reversed and the
spectroscopic metallicities are systematically higher than the
photometric estimates. We are able to determine abundance ratios for
10 chemical elements (Fe, Na, Mg, Al, Ca, Sc, Ti, Cr, Sr, and Ba),
which extend the abundance measurements of chemical elements for RR
Lyrae stars in the Clouds beyond [Fe/H] for the first time. For the
overall [α/Fe] ratio, we obtain an overabundance of 0.36dex,
which is in very good agreement with results from metal-poor stars in
the Milky Way halo as well as from the metal-poor tail in dwarf
spheroidal galaxies. Comparing the abundances with those of the stars
in the Milky Way halo we find that the abundance ratios of stars of
both populations are consistent with another. Therefore, we conclude
that from a chemical point of view early contributions from
Magellanic-type galaxies to the formation of the Galactic halo as
claimed in cosmological models are plausible.
Description:
With the Magellan Echelle (MagE) spectrograph on the 6.5m Magellan
Clay telescope at Las Campanas, Chile, on 2010 January 17 and 18 and
August 4 and 5, we obtain medium resolution (R∼2000-6000) spectra of
six RR Lyrae stars in the LMC and three RR Lyrae stars in the SMC. The
spectrograph has a total wavelength coverage from 3000Å to
10000Å. Three metal-poor standard stars of known metallicity were
observed for comparison: the RR Lyrae star X Arietis (X Ari) and the
non-variable stars HD74000 and G64-12.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 87 9 Properties of RR Lyrae stars observed with
Magellan/MagE
table3.dat 27 10 Various velocity estimates and uncertainties of
all our target stars and X Ari
table4.dat 118 92 Equivalent width measurements for all target
and standard stars
table7.dat 27 12 The final set of parameters from the equivalent
width abundance determination
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See also:
J/ApJS/197/29 : Chemical compositions of 11 RR Lyrae (For+, 2011)
J/AJ/142/61 : RGB stars in LMC outer disk (Carrera+, 2011)
J/ApJ/717/277 : Chemical composition of old LMC clusters (Mucciarelli+, 2010)
J/ApJ/708/560 : Spectroscopy of UMa II and Coma Ber (Frebel+, 2010)
J/AcA/60/165 : VI light curves of SMC RR Lyrae (Soszynski+, 2010)
J/A+A/501/519 : Extremely metal-poor turnoff stars abundances
(Bonifacio+, 2009)
J/AcA/59/1 : VI light curves of LMC RR Lyrae stars (Soszynski+, 2009)
J/A+A/480/379 : Abundances of 59 red giants in LMC (Pompeia+, 2008)
J/ApJ/681/1524 : Detailed abundances for 28 metal-poor stars (Lai+, 2008)
J/AJ/135/836 : Calcium triplet index in LMC stars (Carrera+, 2008)
J/AJ/136/1039 : CaII index of SMC red giant branch stars (Carrera+, 2008)
J/AJ/132/85 : Equivalent width of 33 metal-poor RHB (Preston+, 2006)
J/A+A/460/459 : Radial velocities of LMC RR Lyrae (Borissova+, 2006)
J/AJ/129/1465 : Spectroscopy of red giants in the LMC bar (Cole+, 2005)
J/AJ/128/1177 : Galactic stellar abundances (Venn+, 2004)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
J/A+A/421/937 : Metal abundances of LMC RR Lyrae (Gratton+, 2004)
J/A+A/423/97 : LMC RR Lyrae radial velocities (Borissova+, 2004)
J/A+A/403/1105 : Extremely metal-poor giants equivalent widths
(Francois+,2003)
J/AcA/53/93 : OGLE RR Lyrae in LMC (Soszynski+, 2003)
J/AJ/115/193 : RR Lyrae V light curves (Layden, 1998)
J/AJ/110/2319 : Abundances in RR Lyr variables (Clementini+ 1995)
J/AJ/108/1016 : Kinematics of local RR lyrae stars. I. (Layden, 1994)
J/A+A/290/885 : Abundances of very metal-poor stars (Primas+, 1994)
http://ogle.astrouw.edu.pl/ : OGLE survey
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- MC Magellanic cloud (LMC or SMC)
5- 12 A8 --- Star Name of the RR Lyrae star (1)
14 A1 --- f_Star Flag on Star (a = the observation of RR8645
contains a second, originally not targeted,
star in the slit)
16- 20 F5.2 mag Vmag [18.78/20.21] V-band magnitude
22- 30 F9.7 d Per Period
32- 33 I2 h RAh Hour of Right Ascension (J2000)
35- 36 I2 min RAm Minute of Right Ascension (J2000)
38- 42 F5.2 s RAs Second of Right Ascension (J2000)
44 A1 --- DE- Sign of the Declination (J2000)
45- 46 I2 deg DEd Degree of Declination (J2000)
48- 49 I2 arcmin DEm Arcminute of Declination (J2000)
51- 54 F4.1 arcsec DEs Arcsecond of Declination (J2000)
56- 66 A11 "Y:M:D" Date UT date of observation
68 I1 --- N [1/4] Number of integrations
70- 73 I4 s Exp Exposition time
75- 77 F3.1 arcsec Slit [0.7/2] Slit used for the spectra (2)
79- 83 F5.2 [Sun] [Fe/H]p [-3.5/-2.0] Photometric metallicity
85- 87 A3 --- Bl Blazhko effect? (yes or no)
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Note (1): The star ID of the LMC objects is taken from the identifier in
the Optical Gravitational Lensing Experiment (OGLE III; Udalski et
al., 2008AcA....58...89U 2008AcA....58...89U) data set. For the SMC objects the OGLE II
(Udalski et al., 1997AcA....47..319U 1997AcA....47..319U) identifier is used.
Note (2): We used a 0.7" slit for the spectra of the first three LMC
targets and all of the SMC targets and a 2.0" slit for the other three
LMC RR Lyrae stars. With the 0.7" slit, a resolving power of
R=λ/Δλ∼6000 can be achieved, while the 2.0" slit
has a resolving power of R∼3000.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Star Name of the RR Lyrae star
10- 12 I3 km/s RVh [-40/325] Median heliocentric systemic radial
velocity
14- 16 I3 km/s RVl [-51/309] Systemic radial velocity in the
local standard of rest (LSR)
18- 21 F4.2 --- Phase Mean phase of the observation
23- 24 I2 km/s sr Standard deviation of the radial velocity
measurements (σr)
26- 27 I2 km/s sy Uncertainty of the systemic velocity
(σγ)
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- El Name of ion
6- 9 F4.1 --- Z Atomic number and ionisation
11- 17 F7.2 0.1nm lambda Wavelength λ (Å)
19- 22 F4.2 eV EP Excitation potential
24- 29 F6.3 --- loggf Log of the oscillator strength
31- 35 F5.1 10-13m HD74000(1) ? Equivalent width of HD74000 (mÅ) (1)
37- 40 F4.1 10-13m HD74000(2) ? Equivalent width of HD74000 (mÅ) (2)
42- 46 F5.1 10-13m HD74000(3) ? Equivalent width of HD74000 (mÅ) (3)
48- 52 F5.1 10-13m XAri(1) ? Equivalent width of X Ari; (mÅ) (1)
54- 58 F5.1 10-13m XAri(4) ? Equivalent width of X Ari; (mÅ) (4)
60- 64 F5.1 10-13m G64-12(1) ? Equivalent width of G64-12; (mÅ) (1)
66- 70 F5.1 10-13m RR15903 ? Equivalent width of RR 15903 (mÅ) (1)
72- 76 F5.1 10-13m RR8645 ? Equivalent width of RR 8645 (mÅ) (1)
78- 82 F5.1 10-13m RR1422 ? Equivalent width of RR 1422 (mÅ) (1)
84- 88 F5.1 10-13m RR177 ? Equivalent width of RR 177 (mÅ) (1)
90- 94 F5.1 10-13m RR11371 ? Equivalent width of RR 11371 (mÅ) (1)
96-100 F5.1 10-13m RR22827 ? Equivalent width of RR 22827 (mÅ) (1)
102-106 F5.1 10-13m RR122432 ? Equivalent width of RR 122432 (mÅ) (1)
108-112 F5.1 10-13m RR50180 ? Equivalent width of RR 50180 (mÅ) (1)
114-118 F5.1 10-13m RR143874 ? Equivalent width of RR 143874 (mÅ) (1)
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Note (1): Observed by Haschke et al. (2012AJ....143...48H 2012AJ....143...48H);
Note (2): Observed by Peterson et al. (1978ApJ...222..181P 1978ApJ...222..181P);
Note (3): Observed by Beveridge et al. (1994AJ....108..285B 1994AJ....108..285B);
Note (4): Observed by Clementini et al. (1995, Cat. J/AJ/110/2319).
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Star Star name
10- 13 I4 K Teff Derived effective temperature
15- 17 F3.1 [cm/s2] logg Derived surface graity
19- 23 F5.2 [Sun] [Fe/H] [-3.1/-1.9] Derived metallicity
25- 27 F3.1 km/s vt Microturbulence velocity ξ
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 16-Oct-2013