J/AJ/142/188 Metal-poor stars from the HES using CH G-band (Placco+, 2011)
Searches for metal-poor stars from the Hamburg/ESO survey using the CH G band.
Placco V.M., Kennedy C.R., Beers T.C., Christlieb N., Rossi S.,
Sivarani T., Lee Y.S., Reimers D., Wisotzki L.
<Astron. J., 142, 188 (2011)>
=2011AJ....142..188P 2011AJ....142..188P
ADC_Keywords: Effective temperatures ; Stars, carbon ; Abundances, [Fe/H] ;
Stars, metal-deficient ; Stars, population II
Keywords: Galaxy: halo - stars: abundances - stars: carbon -
stars: Population II - surveys
Abstract:
We describe a new method to search for metal-poor candidates from the
Hamburg/ESO objective-prism survey (HES) based on identifying stars
with apparently strong CH G-band strengths for their colors. The
hypothesis we exploit is that large overabundances of carbon are
common among metal-poor stars, as has been found by numerous studies
over the past two decades. The selection was made by considering two
line indices in the 4300Å region, applied directly to the
low-resolution prism spectra. This work also extends a previously
published method by adding bright sources to the sample. The spectra
of these stars suffer from saturation effects, compromising the index
calculations and leading to an undersampling of the brighter
candidates. A simple numerical procedure, based on available
photometry, was developed to correct the line indices and overcome
this limitation. Visual inspection and classification of the spectra
from the HES plates yielded a list of 5288 new metal-poor (and by
selection, carbon-rich) candidates, which are presently being used as
targets for medium-resolution spectroscopic follow-up. Estimates of
the stellar atmospheric parameters, as well as carbon abundances, are
now available for 117 of the first candidates, based on follow-up
medium-resolution spectra obtained with the SOAR 4.1m and Gemini 8m
telescopes. There are eight newly discovered stars with [Fe/H] < -3.0
in our sample, including two with [Fe/H] < -3.5.
Description:
The observed sample consists of data collected with two different
telescope/spectrograph combinations: 58 star samples from SOAR
(Southern Astrophysics Research) telescope 4.1m/Goodman spectrograph
(observed in 2009B, 2010B, and 2011A semesters in the wavelength range
3550-5500Å and R∼1500) and 59 stars from Gemini 8m telescope (North
and South)/Gemini Multi-Object Spectrograph (GMOS)(2010A and 2011A
semesters with R∼1700).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 66 117 Stellar data for the observed candidates
table4.dat 41 234 Atmospheric parameters and carbonicity estimates
for the observed candidates
table5.dat 96 5288 Candidate metal-poor stars
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
J/A+A/290/885 : Abundances of very metal-poor stars (Primas+, 1994)
J/A+A/300/751 : Metal-poor stars spectroscopy. II (Axer+, 1995)
J/AJ/117/981 : Estimation of stellar metal abundance. II. (Beers+, 1999)
J/AJ/128/2402 : Extremely metal-poor star candidates abundances (Lai+, 2004)
J/ApJS/155/651 : Evolution of extremely metal-poor stars (Herwig+, 2004)
J/AJ/130/2804 : Carbon abundances in metal-poor stars (Rossi+, 2005)
J/AJ/132/137 : Abundances of extremely metal-poor carbon stars (Cohen+, 2006)
J/ApJ/652/1585 : Bright metal-poor stars from HES survey (Frebel+, 2006)
J/ApJ/658/367 : Abundances of carbon stars in Galactic halo (Komiya+, 2007)
J/A+A/490/769 : Yields from extremely metal-poor stars (Campbell+, 2008)
J/A+A/484/721 : HES survey. IV. Candidate metal-poor stars (Christlieb+, 2008)
J/AJ/139/1051 : Metal-poor stars from HES: Paper I (Placco+, 2010)
J/MNRAS/412/843 : SAGA extremely metal-poor stars (Suda+, 2011)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- --- [HE]
4- 12 A9 --- HE Star name in Hamburg/ESO survey (HHMM-DDMM;
equinox B1950))
14- 15 I2 h RAh Hour of Right Ascension (J2000)
17- 18 I2 min RAm Minute of Right Ascension (J2000)
20- 23 F4.1 s RAs Second of Right Ascension (J2000)
25 A1 --- DE- Declination sign (J2000)
26- 27 I2 deg DEd Degree of Declination (J2000)
29- 30 I2 arcmin DEm Arcminute of Declination (J2000)
32- 33 I2 arcsec DEs Arcsecond of Declination (J2000)
35- 38 F4.1 mag Bmag [10.5/16] HES photographic B magnitude derived
from Hamburg/ES0 DSS-I BJ plates
40- 43 F4.2 mag (J-K)0 [0.26/0.85] Intrinsic 2MASS deredenned J-K
color index (1)
45- 48 F4.1 0.1nm GPE GP index, 15Å wide G-band index (G2)
50- 54 F5.2 0.1nm EGP EGP index (G3)
56- 61 A6 --- Tel Telescope (SOAR or Gemini) (2)
63- 66 A4 --- Tag Remarks and notes (G4)
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Note (1): Calculated based on the Schlegel et al. (1998ApJ...500..525S 1998ApJ...500..525S)
prescription.
Note (2): SOAR = Southern Astrophysics Research Telescope.
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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 --- --- [HE]
4- 12 A9 --- HE Star name in Hamburg/ESO survey (HHMM-DDMM)
14- 19 F6.1 km/s RV [-401.7/442.5] Radial Velocity
21- 24 I4 K Teff [4028/7604] Effective temperature
26- 29 F4.2 [cm/s2] logg [1/4.98] Surface gravity
31- 35 F5.2 [Sun] [Fe/H] [-3.8/0] Metallicity
37- 41 F5.2 [Sun] [C/Fe] [-0.36/3.65] Carbonicity (1)
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Note (1): Obtained with the same procedure described in Paper I
(Cat. J/AJ/139/1051) using spectral synthesis in the G-band region.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- --- [HE]
4- 12 A9 --- HE Star name in Hamburg/ESO survey (HHMM+DDMM)
14- 33 A20 --- HESID Unique HES identifier (HEHHMMSSmDDMMSSaNNNN)
35- 36 I2 h RAh Hour of Right Ascension (J2000)
38- 39 I2 min RAm Minute of Right Ascension (J2000)
41- 44 F4.1 s RAs Second of Rigth Ascension (J2000)
46 A1 --- DE- [-] Sign of the Declination (J2000)
47- 48 I2 deg DEd Degree of Declination (J2000)
50- 51 I2 arcmin DEm Arcminute of Declination (J2000)
53- 54 I2 arcsec DEs Arcsecond of Declination (J2000)
56- 61 A6 --- obj Object type (stars or bright) (1)
63- 66 F4.1 mag Bmag [10/18.3] HES photographic B magnitude
68- 71 F4.2 mag (B-V)0 [0.32/1.48] Intrinsic (B-V)0 color index
73- 76 F4.2 mag (J-K)0 [0.2/0.7] Intrinsic (J-K)0 color index (G1)
78- 80 F3.1 0.1nm KP [0/9] KP index, measured in HES spectrum (2)
82- 85 F4.1 0.1nm GPE [31/72] GPE index, measured in HES spectrum (G2)
87- 91 F5.2 mag EGP EGP index, measured in HES spectrum (G3)
93- 96 A4 --- Cand Candidate class (G4)
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Note (1): The present study made use of two classes of objects extracted from
the HES objective-prism plates: stars and bright objects. The stars are
point-like sources showing no signs of saturation in their spectra and the
bright sources are objects close to (and above) the saturation threshold of
the HES plates. For each of these types, a different set of restrictions was
developed, including a more relaxed version of the method described in
Christlieb et al. (2008, Cat. J/A+A/484/721), and applied to the database in
order to reduce the number of spurious candidates for subsequent analysis.
See section 3.1.
Note (2): The KP line index measures the strength of the CaII line, defined
by Beers et al. (1999, Cat. J/AJ/117/981).
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Global notes:
Note (G1): The J and K magnitudes were taken from the 2MASS All-Sky Data Release
(Skrutskie et al. 2006, Cat. VII/233).
Note (G2): GPE = GP Extended. Line index for the CH band. This index is a
pseudo-equivalent width that measures the contrast between the
observed spectra and the continuum level.
Note (G3): New index consisting of a flux ratio, integrated in intervals
defined for both the line band and the red sideband. Defined in
equation (1): EGP=-2.5log(I[4200-4400]/I[4425-4520])
where I[x-y] represents the integrated flux in wavelength range x to yi
(wavelength in Å=0.1nm)
Note (G4): Classes/notes as follows:
mpca = Absent CaII K line;
mpcb = Weak CaII K line;
mpcc = Strong CaII K line;
unid = CaII K line not found;
fhlc = Faint high latitude carbon stars;
habs = Strong absorption H lines;
hbab = Horizontal-branch/A-type star;
nois = Low signal-to-noise ratio (SNR);
ovl = Overlapping spectra;
art = Artifacts on photographic plates;
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History:
From electronic version of the journal
References:
Placco et al. Paper I 2010AJ....139.1051P 2010AJ....139.1051P Cat. J/AJ/139/1051
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 21-Mar-2013