Vertical distribution of Galactic disk stars

Abstract

We present the parameters of 891 stars, mostly clump giants, including atmospheric parameters, distances, absolute magnitudes, spatial velocities, galactic orbits and ages. One part of this sample consists of local giants, within 100 pc, with atmospheric parameters either estimated from our spectroscopic observations at high resolution and high signal-to-noise ratio, or retrieved from the literature. The other part of the sample includes 523 distant stars, spanning distances up to 1 kpc in the direction of the North Galactic Pole, for which we have estimated atmospheric parameters from high resolution but low signal-to-noise Echelle spectra. This new sample is kinematically unbiased, with well-defined boundaries in magnitude and colours. We revisit the basic properties of the Galactic thin disk as traced by clump giants. We find the metallicity distribution to be different from that of dwarfs, with fewer metal-rich stars. We find evidence for a vertical metallicity gradient of -0.31 dex kpc −1 and for a transition at ∼4-5 Gyr in both the metallicity and velocities. The age-metallicity relation (AMR), which exhibits a very low dispersion, increases smoothly from 10 to 4 Gyr, with a steeper increase for younger stars. The age-velocity relation (AVR) is characterized by the saturation of the V and W dispersions at 5 Gyr, and continuous heating in U.

Chemical Cartography With Apogee: Large-Scale Mean Metallicity Maps of the Milky Way Disk

“…Soubiran et al (2008) measure a slope of −0.31 ± 0.03 dex kpc −1 for their sample of red clump giants that span a range of populations, in good agreement with our measurement of −0.305 ± 0.011 dex kpc −1 for the entire sample. Note that the measured gradient at R = 2 kpc and R = 4 kpc are the most likely to be affected by a metallicity bias.…”

“…The slope of the vertical gradient has been measured to be −0.22 dex kpc −1 (Ak et al 2007) for |z| < 3 kpc in a sample of high-latitude G dwarfs from DR5 (Adelman-McCarthy et al 2007) of the SDSS, −0.22 dex kpc −1 in a sample of horizontalbranch stars (Chen et al 2011) from DR8 (Aihara et al 2011), and −0.14 dex kpc −1 from a sample of kinematically selected thick-disk F/G/K dwarfs (Kordopatis et al 2011). For samples targeting stars closer to the disk, Chen et al (2003) measure a slope of −0.295 dex kpc −1 using open clusters, Bartašiūtė et al (2003) obtain −0.23 dex kpc −1 for a sample of thin-disk stars identified by kinematics and asymmetric drift, Marsakov & Borkova (2006) find a slope of −0.29 dex kpc −1 for thin-disk stars selected based on chemistry and orbital parameters, and Soubiran et al (2008) measure a slope of −0.31 dex kpc −1 for |z| < 1 kpc from a sample of red clump giants.…”

Climbing the cosmic ladder with stellar twins

“…Soubiran, Bienaymé & Siebert (2003) introduced this concept to determine the atmospheric parameters and absolute magnitude of a star by computing a likelihood function of the difference between its spectrum and a grid of observed spectra of stars with parallaxes. The reported distances errors are less than 30% for when compared with Hipparcos parallaxes of FGK stars (Katz et al 2011) and less than 12% when red clump stars are considered (Soubiran et al 2008). This compares well with other methods but in this case the distances rely on interpolations in the parameter space to compute the likelihood function and not on stellar evolution and atmosphere models.…”

Spiral arm kinematics for Milky Way stellar populations

“…The study of the local vertical profiles of the MW disks has long tradition and is still pushed mostly under axisymmetric assumption (e.g., Just & Jahreiß 2010;Just, Gao & Vidrih 2011;Soubiran, Bienaymé & Siebert 2003;Siebert, Bienaymé & Soubiran 2003;Bienaymé et al 2006;Soubiran et al 2008). The study of the vertical kinematics of spiral arms is still an open research field (e.g., Williams et al 2013;Widrow et al 2012).…”