C stars as kinematic probes of the Milky Way disk from 9 to 15 kpc

Abstract

Context. The availability, from 2MASS, of a large homogeneous sample of Galactic C stars and the recognition that their absolute magnitude can be accurately determined offer the possibility to use them as kinematical probes to investigate motions in the thin or thick disks. Aims. Determine the radial velocities for 70 C stars, a few degrees from the Galactic plane and distributed in longitudes from 60 • to 220 • . Methods. Spectra, with a resolution of 4300, were obtained with the DAO 1.8 m telescope during 6 beautiful nights in October 2006. Results. The rotation velocities of C stars with 60 • < < 150 • suggest a flat rotation curve to 15 kpc. A number of stars have velocities that do not fit the thin disk rotation. Some of them, toward = 200 • are most probably members of the Canis Major overdensity. Conclusions. Effort should be made to extend the rotation curve to more that 20 kpc.Key words. stars: carbon -stars: kinematics -Galaxy: disk -Galaxy: kinematics and dynamics IntroductionThe importance of galactic potentials in shaping the chemodynamical evolution of stellar populations is well known. Unfortunately, the surface mass distribution of the Milky Way is still poorly constrained, even while our knowledge of Galactic stellar abundance distributions grows ever more detailed. One reason for this shortcoming is the difficulty of determining the Galactic rotation curve in the outer disk.Recently, Carignan et al. (2006) which they might have been born but still relatively young, with smaller random velocities than older tracers (e.g. planetary nebulae). They are believed to be members of the thin disk population (e.g. Feast et al. 2006).In the late 80's, Aaronson and collaborators recognized that C stars could be useful bright kinematical probes (Aaronson et al. 1989(Aaronson et al. , 1990. They collected hundreds of radial velocities of disk (b ≈ 0 • ) C stars, with JHK photometry. The fact that these C stars were extremely unevenly distributed in galactic latitude made the interpretation of their results unreliable (Schechter et al. 1988). A study of the kinematics of the C stars toward the anticenter was published by Metzger & Schechter (1994). Beside the untimely death of Aaronson we believe there are two main reasons why these data never yielded significant insights in the kinematics of the outer disk: 1) the selection of C stars from objective-prism spectra leads to highly inhomogeneous samples containing faint bluish C stars mixed with brighter genuine N-type C stars (see Demers et al. 2002) thus artificially increasing the observed K absolute magnitude spread; 2) the estimate of distances and colors for stars with b ≈ 0 • requires a quite accurate knowledge of the extinction across the disk.More recently, Nakashima et al. (2000) obtained the rotation curve of the outer disk using the radial velocity of a few C-and O-rich SiO maser emission Miras located very close to the Galactic plane. Absolute I magnitudes were deduced from the Mira's P − L relation. Not knowing individual reddening, the a...

The outskirts of Cygnus OB2

“…This is partly caused by their intrinsically redder spectral energy distributions, but the dominant factor is their larger average distances due to their brighter infrared absolute magnitudes. Whereas we expect OB stars in Cygnus OB2 to have absolute magnitudes in the -3 < M K < −5.5 range (Martins & Plez 2006), cool red giants are expected to reach M K = −7 (e.g., Ferraro et al 2000), long period variables are in the range Knapp et al 2003), and carbon stars usually have M K < −8 (Weinberg & Nikolaev 2001;Demers & Battinelli 2007). They are thus easily detectable at the distance of the Perseus arm and beyond in a magnitude-limited sample like ours.…”

The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution

“…To compare those earlier results with ours, we have used the data (i.e. distances, radial velocities and errors) of H II regions published by Fich et al (1989) and those of carbon stars of 60 l 150 • published by Demers & Battinelli (2007), and recalculate the circular velocities, adopting the same value of R0 assumed in the current study, the value of Vc(R0) deduced from the current study, as well as the solar peculiar velocities in the radial and vertical directions (U⊙, W⊙) from Huang et al (2015b) for consistency reason. The results are presented in Fig.…”

Tracing the tidal streams of the Sagittarius dSph, and halo Milky Way features, with carbon-rich long-period variables

“…The strong band heads also aid velocity determination (Aaronson 1983), making them good kinematic probes. For example, they have been used to study the kinematics of the outer regions of the Galactic disk (Demers & Battinelli 2007), the Galactic halo (Hartwick & Cowley 1985;Mould et al 1985;Bothun et al 1991;Green et al 1994 The population of carbon stars is composed of a complex "zoo" of many types and with a variety of origins (Abia et al 2003), and whose original classification was determined by the presence of certain spectroscopic features. N-type stars have substantial absorption at the blue end of the spectrum, while R-types stars still show the blue end of the spectrum, and CH stars have strong CH absorption.…”