Precise radial velocities of giant stars. III. Spectroscopic stellar parameters

By S. Hekker, Jorge Meléndez. 2007

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Context. A radial velocity survey of about 380 G and K giant stars is ongoing at Lick observatory. For each star we have a high signal to noise ratio template spectrum, which we use to determine spectroscopic stellar parameters. Aims. The aim of this paper is to present spectroscopic stellar parameters, i.e. effective temperature, surface gravity, metallicity and rotational velocity for our sample of G and K giant stars. Methods. Effective temperatures, surface gravities and metallicities are determined from the equivalent width of iron lines, by imposing excitation and ionisation equilibrium through stellar atmosphere models. Rotational velocities are determined from the full width at half maximum (FWHM) of moderate spectral lines. A calibration between the FWHM and total broadening (rotational velocity and macro turbulence) is obtained from stars in common between our sample and the sample from Gray (1989, ApJ, 347, 1021). Macro turbulence is determined from the macro turbulence vs. spectral type relations from Gray (2005, The Observation and Analysis of Stellar Photospheres). Results. The metallicity we derive is essentially equal to the literature values, while the effective temperature and surface gravity are slightly higher by 56 K and 0.15 dex, respectively. A method comparison is performed with 72 giants in common with Luck & Heiter (2007, AJ, 133, 2464), which shows that both methods give similar results. Our rotational velocities are comparable with those obtained by Gray (1989, ApJ, 347, 1021), but somewhat higher than those of de Medeiros & Mayor (1999, A&AS, 139, 433), which is consistent with the different diagnostics used to determine them. Conclusions. We are able to determine spectroscopic stellar parameters for about 380 G and K giant stars uniformly (112 stars are being analysed spectroscopically for the first time). For stars available in the literature, we find reasonable agreement between literature values and values determined in the present work. In addition, we show that the metallicity enhancement of companion hosting stars might also be valid for giant stars, with the planet hosting giants being 0.13 ± 0.03 dex (i.e. 35 ± 10%) more metal rich than our total sample of stars.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/c1ccdbbf972c369c3f3a27e521c03d9eaa47bfc2

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Citations in the corpus

The PASTEL catalogue of stellar parameters (2010, background): “– Hekker= Hekker & Meléndez (2007), 366 stars – Luck= Luck & Heiter (2006, 2007), 222 stars – McWilliam =McWilliam (1990), 671 stars – Mishenina = Mishenina & Kovtyukh (2001); – Ramı́rez= Ramı́rez et al. (2007), 523 stars – Valenti= Valenti & Fischer (2005) , 1040 stars studies can be considered…”
Stellar Parameters and Elemental Abundances of Late-G Giants (2008, methodology): “…(1990) adopted the direct g-determination method [from L, Teff , and M (estimated from evolutionary tracks)], while the spectroscopic method based on Fe i and Fe ii lines (similar to that we used) was invoked by da Silva et al. (2006), Luck and Heiter (2007),8, and Hekker and Meléndez (2007).”
Gaia FGK benchmark stars: Effective temperatures and surface gravities (2015, background): “Furthermore, Hekker & Meléndez (2007) compared in their Fig.”
Coudé-feed stellar spectral library – atmospheric parameters (2010, methodology): “The temperatures given by Hekker & Meléndez (2007) are ∼240 K hotter.”
Chemical similarities between Galactic bulge and local thick disk red giants: O, Na, Mg, Al, Si, Ca, and Ti (2010, methodology): “A preliminary version of our line list (Hekker & Meléndez 2007) has been tested in∼380 field (Hekker & Meléndez 2007) and 39 open cluster (Santos et al. 2009) giants, and the final list has been already used in field bulge (Ryde et al. 2009b) and globular cluster (Meléndez & Cohen 2009) giants.”
Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer (2017, unknown): “…spectral type; (5) Le Borgne et al. (2003), (6) Houdashelt et al. (2000), (7) Katz et al. (2011), (8) Valdes et al. (2004), (9) Soubiran et al. (2016), (10)Milone et al. (2011), (11) Prugniel et al. (2011), (12) Bordé et al. (2002), (13) Hekker & Meléndez (2007), and (14) Hohle et al. (2010).”
Precise Radial Velocities of Giant Stars VII. Occurrence Rate of Giant Extrasolar Planets as a Function of Mass and Metallicity (2014, background): “While Pasquini et al. (2007), Takeda et al. (2008) and Mortier et al. (2013) do not find evidence for such a correlation in their samples of G and K giants, Hekker & Meléndez (2007) find indications for a positive correlation between metallicity and planet occurrence rate for K giant stars.”
ULySS: a full spectrum fitting package (2009, background): “Another recent spectroscopic analysis gives:Teff=4150 log(g)=1.70 [Fe/H]=-0.41 (Hekker & Meléndez 2007); and interferometric measurements tend to indicate a lowerTeff : 3650 – 3800 K, and hence probably lower gravity log(g)= 0.9 (Neilson & Lester 2008; Wittkowski et al. 2006).”
SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs - I. New atmospheric parameters and masses for 48 stars with planets (2013, background): “Although the exact reasons are still not clear, these problems may have even lead to a significant discrepancy in studies done by different authors concerning the metallicitygiant planet correlation in giants (see debate in Pasquini et al. 2007; Hekker & Meléndez 2007; Ghezzi et al. 2010a).”
Radial Velocity Search for Extrasolar Planets in Visual Binary Systems (2009, background): “A typical microturbulent velocity of a giant with log g = 1.30 is 2–3 km s 1 (Hekker & Meléndez 2007).”