J/A+A/633/A129 ESPRESSO radial velocities of HE0107-5240 (Bonifacio+, 2020)
ESPRESSO highlights the binary nature of the ultra-metal-poor giant HE0107-5240.
Bonifacio P., Molaro P., Adibekyan V., Aguado D., Alibert Y.,
Allende Prieto C., Caffau E., Cristiani S., Cupani G., Di Marcantonio P.,
D'Odorico V., Ehrenreich D., Figueira P., Genova R.,
Gonzalez Hernandez J.I., Lo Curto G., Lovis C., Martins C.J.A.P., Mehner A.,
Micela G., Monaco L., Nunes N.J., Pepe F.A., Poretti E., Rebolo R.,
Santos N.C., Saviane I., Sousa S., Sozzetti A., Suarez-Mascareno A.,
Udry S., Zapatero-Osorio M.R.
<Astron. Astrophys. 633, A129 (2020)>
=2020A&A...633A.129B 2020A&A...633A.129B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Radial velocities
Keywords: binaries: spectroscopic - stars: abundances - Galaxy: abundances -
Galaxy: halo
Abstract:
The vast majority of the known stars of ultra low metallicity
([Fe/H]←4.5) are known to be enhanced in carbon, and belong to the
'low-carbon band' (A(C)=log(C/H)+12∼7.6). It is generally, although
not universally, accepted that this peculiar chemical composition
reflects the chemical composition of the gas cloud out of which these
stars were formed. The first ultra-metal-poor star discovered, HE
0107-5240, is also enhanced in carbon and belongs to the 'low-carbon
band'. It has recently been claimed to be a long-period binary, based
on radial velocity measurements. It has also been claimed that this
binarity may explain its peculiar composition as being due to mass
transfer to a former AGB companion. Theoretically, low-mass ratios in
binary systems are much more favoured amongst Pop III stars than they
are amongst solar-metallicity stars. Any constraint on the mass ratio
of a system of such low metallicity would shed light on the star
formation mechanisms in this metallicity regime.
We acquired one high precision spectrum with ESPRESSO in order to
check the reality of the radial velocity variations. In addition we
analysed all the spectra of this star in the ESO archive obtained with
UVES to have a set of homogenously measured radial velocities.
The radial velocities were measured using cross correlation against a
synthetic spectrum template. Due to the weakness of metallic lines in
this star, the signal comes only from the CH molecular lines of the
G-band.
The measurement obtained in 2018 from an ESPRESSO spectrum
demonstrates unambiguously that the radial velocity of HE 0107-5240
has increased from 2001 to 2018. Closer inspection of the measurements
based on UVES spectra in the interval 2001-2006 show that there is a
96% probability that the radial velocity correlates with time, hence
the radial velocity variations can already be suspected from the UVES
spectra alone.
We confirm the earlier claims of radial velocity variations in
HE 0107-5240. The simplest explanation of such variations is that the
star is indeed in a binary system with a long period. The nature of
the companion is unconstrained and we consider it is equally probable
that it is an unevolved companion or a white dwarf. Continued
monitoring of the radial velocities of this star is strongly
encouraged.
Description:
A new measurement of the radial velocity of the ultra-metal-poor star
HE 0107-5240 is derived using a high resolution spectrum obtained with
the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic
Observations (ESPRESSO). In the high resolution mode there are two
fibres with a core diameter of 140um that corresponds to 1.0" on
the sky. HE 0107-5240 was observed on September 3, 2018. The new
measurement is put into context with measurements derived using
spectra taken in the last 17 years and confirms the variation in
radial velocity of this star over this period.
Objects:
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RA (2000) DE Designation(s)
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01 09 29.16 -52 24 34.2 HE 0107-5240 = UCAC2 9168846
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 113 14 Literature data on all stars with [Fe/H]←4.5
table2.dat 79 38 Radial velocities of HE 0107-5240
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 24 A24 --- Name Name of the star
26- 27 I2 h RAh Right ascension (J2000)
29- 30 I2 min RAm Right ascension (J2000)
32- 35 F4.1 s RAs Right ascension (J2000)
37 A1 --- DE- Declination sign (J2000)
38- 39 I2 deg DEd Declination (J2000)
41- 42 I2 arcmin DEm Declination (J2000)
44- 45 I2 arcsec DEs Declination (J2000)
47- 50 I4 K Teff effective temperature
52- 54 F3.1 [cm/s2] logg logarithm of the surface gravity
56 A1 --- l_[Fe/H] Limit flag for upper limits
(< is upper limit, blank is measure)
57- 61 F5.2 [-] [Fe/H] logarithmic iron abundance with respect
to the Sun
63 A1 --- l_A(C) Limit flag for upper limits
(< is upper limit, blank is measure)
64- 67 F4.2 [-] A(C) logarithmic carbon abundance
69 A1 --- l_A(Li) Limit flag for upper limits
(< is upper limit, blank is measure)
70- 73 F4.2 [-] A(Li) ? logarithmic lithium abundance
75-113 A39 --- Ref References
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 10 A10 "date" Obs.date Date of observation
12- 22 F11.5 d MJD Modified Julian date at the start of
the exposure
24- 31 A8 -- Instr Instrument that obtained the spectrum
34- 36 I3 nm CW ? Central wavelength of the spectrum
38- 44 F7.3 km/s RV ? Measured geocentric radial velocity
46- 52 F7.3 km/s Bcorr ? Barycentric correction
54- 59 F6.3 km/s Tcorr ? Correction based on telluric lines
61- 65 F5.3 km/s e_Tcorr ? Error on the correction based on
telluric lines
67- 73 F7.3 km/s BRV Barycentric radial velocity
75- 79 F5.3 km/s e_BRV Estimated error on the barycentric
radial velocity
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Acknowledgements:
Piercarlo Bonifacio, Piercarlo.Bonifacio(at)obspm.fr
(End) Piercarlo Bonifacio [GEPI, France], Patricia Vannier [CDS] 20-Jan-2020