J/MNRAS/489/5900 Extremely metal-poor stars in SkyMapper DR1.1 (Da+, 2019)
The SkyMapper DR1.1 search for extremely metal-poor stars.
Da Costa G.S., Bessell M.S., Mackey A.D., Nordlander T., Asplund M.,
Casey A.R., Frebel A., Lind K., Marino A.F., Murphy S.J., Norris J.E.,
Schmidt B.P., Yong D.
<Mon. Not. R. Astron. Soc., 489, 5900-5918 (2019)>
=2019MNRAS.489.5900D 2019MNRAS.489.5900D (SIMBAD/NED BibCode)
ADC_Keywords: Abundances, [Fe/H] ; Stars, metal-deficient ;
Stars, population II ; Milky Way ; Photometry, ugriz ;
Spectra, optical
Keywords: stars: abundances - stars: Population II - Galaxy: halo -
Galaxy: stellar content
Abstract:
We present and discuss the results of a search for extremely
metal-poor stars based on photometry from data release DR1.1 of the
SkyMapper imaging survey of the southern sky. In particular, we
outline our photometric selection procedures and describe the
low-resolution (R∼3000) spectroscopic follow-up observations that are
used to provide estimates of effective temperature, surface gravity,
and metallicity ([Fe/H]) for the candidates. The selection process is
very efficient: of the 2618 candidates with low-resolution spectra
that have photometric metallicity estimates less than or equal to
-2.0, 41 per cent have [Fe/H]=←2.75 and only approximately seven per
cent have [Fe/H]>-2.0dex. The most metal-poor candidate in the sample
has [Fe/H]←4.75 and is notably carbon rich. Except at the lowest
metallicities ([Fe/H]←4), the stars observed spectroscopically are
dominated by a 'carbon-normal' population with [C/Fe]1D,LTE=<+1dex.
Consideration of the A(C)1D,LTE versus [Fe/H]1D,LTE diagram
suggests that the current selection process is strongly biased against
stars with A(C)1D,LTE>7.3 (predominantly CEMP-s) while any bias
against stars with A(C)1D,LTE<7.3 and [C/Fe]1D,LTE>+1
(predominantly CEMP-no) is not readily quantifiable given the
uncertainty in the SkyMapper v-band DR1.1 photometry. We find that the
metallicity distribution function of the observed sample has a
power-law slope of Δ(LogN)/Δ[Fe/H]=1.5±0.1dex per dex
for -4.0=<[Fe/H]=←2.75, but appears to drop abruptly at [Fe/H]~-4.2,
in line with previous studies.
Description:
We have used a combination of SkyMapper DR1.1 photometry (Wolf et al.
2018PASA...35...10W 2018PASA...35...10W, Cat. II/358) and low-resolution spectroscopic
follow-up with the ANU 2.3m telescope to identify EMP stars in the
Galactic halo.
Commencing in 2016 February we have observed SkyMapper photometric EMP
candidates with the ANU 2.3m telescope at Siding Spring Observatory on
a regular basis. The program has been allocated approximately six
nights per month and useful data have been obtained for ∼60 per cent
of the time.
By deliberate choice of the colour range for the candidate stars, the
survey targets EMP giants. It has proved to be a very efficient
approach with over 40 per cent of the photometric candidates having
[Fe/H]=←2.75 as derived from the low-resolution spectra. The
low-resolution spectra allow the identification of 142 stars within
the selection window boundaries that have [Fe/H]fitter←3.0 and
which, to our knowledge, have not been previously studied. The
parameters for these stars are given in Table 2 while Table 3 gives
the same data for a further 29 candidates whose DR1.1 photometry falls
outside the selection window or which fail the adopted DR1.1
photometric selection criteria (see Section 2 for the photometric
selection).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 79 30 Comparison of [Fe/H]fitter values with those
from high-dispersion spectroscopy literature
values
table2.dat 124 142 Details of the derived parameters for the
observed stars with [Fe/H]fitter←3.0
table3.dat 92 29 Details of the derived parameters for additional
candidates with [Fe/H]fitter←3.0
--------------------------------------------------------------------------------
See also:
II/358 : SkyMapper Southern Sky Survey. DR1.1 (Wolf+, 2018)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- Name Star name
26- 30 F5.2 [-] [Fe/H]hd Fe/H abundance ratio from high-dispersion
spectroscopy from literature
32- 36 F5.2 [-] [Fe/H]f Fe/H abundance ratio from the
spectrophotometric fits to the 2.3m
low-resolution WiFeS spectroscopy
38- 77 A40 --- r_[Fe/H]hd References for [Fe/H]hd
79 A1 --- f_Name Flag on Name (1)
--------------------------------------------------------------------------------
Note (1): Flag as follows:
1 = Star has [C/Fe]~+2.6, 2.3m spectroscopic fits modified to exclude
strong CH features
2 = Star has [C/Fe]~+2.3, 2.3m spectroscopic fits modified to exclude
strong CH features
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- Name Star name (SMSS JHHMMSS.ss-DDMMSS.s)
26- 27 I2 h RAh Right ascension (J2000)
29- 30 I2 min RAm Right ascension (J2000)
32- 36 F5.2 s RAs Right ascension (J2000)
38 A1 --- DE- Declination sign (J2000)
39- 40 I2 deg DEd Declination (J2000)
42- 43 I2 arcmin DEm Declination (J2000)
45- 48 F4.1 arcsec DEs Declination (J2000)
50- 55 F6.3 mag gmag SkyMapper DR1.1 g-band magnitude
57- 61 F5.3 mag g-i SkyMapper DR1.1 (g-i)0 colour index
63- 68 F6.3 mag mi Metallicity index (G1)
70- 74 F5.2 0.1nm EW(G) G-band equivalent width
76- 79 I4 K Teff Effective temperature from FITTER
81- 85 F5.3 [cm/s2] logg Surface gravity from FITTER
87- 91 F5.2 [-] [Fe/H]f Fe/H abundance ratio from the
spectrophotometric fits to the 2.3m
low-resolution WiFeS spectroscopy
93- 95 A3 --- f_Name Flag on Name (1)
97-124 A28 --- OName Alternative name
--------------------------------------------------------------------------------
Note (1): Flag as follows:
1 = High dispersion spectroscopic follow-up in Nordlander et al.
(2019MNRAS.488L.109N 2019MNRAS.488L.109N)
2 = High dispersion spectroscopic follow-up in Yong et al. (2019, in
preparation)
3 = Alternative ID for this star is given in column OName
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- Name Star name (SMSS JHHMMSS.ss-DDMMSS.s)
26- 27 I2 h RAh Right ascension (J2000)
29- 30 I2 min RAm Right ascension (J2000)
32- 36 F5.2 s RAs Right ascension (J2000)
38 A1 --- DE- Declination sign (J2000)
39- 40 I2 deg DEd Declination (J2000)
42- 43 I2 arcmin DEm Declination (J2000)
45- 48 F4.1 arcsec DEs Declination (J2000)
50- 55 F6.3 mag gmag SkyMapper DR1.1 g-band magnitude
57- 61 F5.3 mag g-i SkyMapper DR1.1 (g-i)0 colour index
63- 68 F6.3 mag mi Metallicity index (G1)
70- 73 F4.2 0.1nm EW(G) G-band equivalent width
75- 78 I4 K Teff Effective temperature from FITTER
80- 84 F5.3 [cm/s2] logg Surface gravity from FITTER
86- 90 F5.2 [-] [Fe/H]f Fe/H abundance ratio from the
spectrophotometric fits to the 2.3m
low-resolution WiFeS spectroscopy
92 I1 --- f_Name Flag on Name (1)
--------------------------------------------------------------------------------
Note (1):
1 = Fails one of more DR1.1 photometric selection criteria
2 = Lies outside selection window (may also have failed photometric
selection criteria)
--------------------------------------------------------------------------------
Global Notes:
Note (G1): The metallicity index is computed as mi=(v-g)0-1.5(g-i)0
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 20-Jan-2023