Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userInterstellar medium, young stars, and astrometric binaries in Galactic archaeology spectroscopic surveys
88
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Current ongoing stellar spectroscopic surveys (RAVE, GALAH, Gaia-ESO, LAMOST, APOGEE, Gaia) are mostly devoted to studying Galactic archaeology and structure of the Galaxy. But they allow for important auxiliary science: (i) Galactic interstellar medium can be studied in four dimensions (position in space + radial velocity) through weak but numerous diffuse insterstellar bands and atomic absorptions seen in spectra of background stars, (ii) emission spectra which are quite frequent even in field stars can serve as a good indicator of their youth, pointing e.g. to stars recently ejected from young stellar environments, (iii) astrometric solution of the photocenter of a binary to be obtained by Gaia can yield accurate masses when joined by spectroscopic information obtained serendipitously during a survey. These points are illustrated by first results from the first three surveys mentioned above. These hint at the near future: spectroscopic studies of the dynamics of the interstellar medium can identify and quantify Galactic fountains which may sustain star formation in the disk by entraining fresh gas from the halo; RAVE already provided a list of ~14,000 field stars with chromosperic emission in Ca II lines, to be supplemented by many more observations by Gaia in the same band, and by GALAH and Gaia-ESO observations of Balmer lines; several millions of astrometric binaries with periods up to a few years which are being observed by Gaia can yield accurate masses when supplemented with measurements from only a few high-quality ground based spectra.
rate research
Read More
I present an overview of the science goals and achievements of ongoing spectroscopic surveys of individual stars in the nearby Universe. I include a brief discussion of the development of the field of Galactic Archaeology - using the fossil record in old stars nearby to infer how our Galaxy evolved and place the Milky Way in cosmological context.
The ongoing Gaia mission of ESA will provide accurate spatial and kinematical information for a large fraction of stars in the Galaxy. Interstellar extinction and line absorption studies toward a large number of stars at different distances and directions can give a 3-dimensional distribution map of interstellar absorbers, and thus reach a similar spatial perfection. Under certain morphologies (e.g. geometrically thin absorption curtains) one can infer a complete velocity vector from its radial velocity component and so obtain a dynamical information comparable to stars. But observations of a large number of stars at different distances are needed to determine the location of the absorption pockets. Therefore, techniques to measure interstellar absorptions towards (abundant) cool stars are needed. A complex mix of colliding absorption clouds is found in the Galactic plane. Thus, one would wish to start with deep observations to detect the weak, but simpler interstellar absorptions at high Galactic latitudes. Finally, interstellar atomic line absorption studies toward cool stars in the optical are largely limited to Sodium and Potassium doublets, not covered by many surveys, including Gaia. Diffuse interstellar bands can give the same type of information as interstellar atomic absorption lines. A combination of both may also point to differences in dynamics of different components of the interstellar medium. In particular, the Gaia DIB at 862 nm can be used to build absorption maps, as already demonstrated by RAVE. Additionally, several ground-based surveys (e.g APOGEE, Gaia-ESO and Galah) are upgrading this approach. The use of this new information can change our understanding in many areas (e.g. determination of membership of stars in clusters, studies of a few Myr old supernova remnants and investigations of Galactic fountains).
As part of our search for new low-mass members of nearby young moving groups (YMG), we discovered three low-mass, spectroscopic binaries, two of which are not kinematically associated with any known YMG. Using high-resolution optical spectroscopy, we measure the component and systemic radial velocities of the systems, as well as their lithium absorption and H$alpha$ emission, both spectroscopic indicators of youth. One system (2MASS J02543316-5108313, M2.0+M3.0) we confirm as a member of the 40 Myr old Tuc-Hor moving group, but whose binarity was previously undetected. The second young binary (2MASS J08355977-3042306, K5.5+M1.5) is not a kinematic match to any known YMG, but each component exhibits lithium absorption and strong and wide H$alpha$ emission indicative of active accretion, setting an upper age limit of 15 Myr. The third system (2MASS J10260210-4105537, M1.0+M3.0) has been hypothesized in the literature to be a member of the 10 Myr old TW Hya Association (TWA), but with our measured systemic velocity, shows the binary is in fact not part of any known YMG. This last system also has lithium absorption in each component, and has strong and variable H$alpha$ emission, setting an upper age limit of 15 Myr based on the lithium detection.
We present estimates of stellar age and mass for 0.93 million Galactic disk main sequence turn-off and sub-giant stars from the LAMOST Galactic Spectroscopic Surveys. The ages and masses are determined by matching with stellar isochrones using Bayesian algorithm, utilizing effective temperature $T_{rm eff}$, absolute magnitude ${rm M}_V$, metallicity [Fe/H] and $alpha$-element to iron abundance ratio [$alpha$/Fe] deduced from the LAMOST spectra. Extensive examinations suggest the age and mass estimates are robust. The overall sample stars have a median error of 34 per cent for the age estimates, and half of the stars older than 2,Gyr have age uncertainties of only 20--30 per cent. Median error for the mass estimates of the whole sample stars is $sim8$ per cent. The huge dataset demonstrates good correlations among stellar age, [Fe/H] ([$alpha$/H]) and [$alpha$/Fe]. Particularly, double sequence features are revealed in the both the age--[$alpha$/Fe] and age--[Fe/H]([$alpha$/H]) spaces. In the [Fe/H]--[$alpha$/Fe] space, stars of 8--10,Gyr exhibit both the thin and thick disk sequences, while younger (older) stars show only the thin (thick) disk sequence, indicating that the thin disk became prominent 8--10,Gyr ago, while the thick disk formed earlier and almost quenched 8,Gyr ago. Stellar ages exhibit positive vertical and negative radial gradients across the disk, and the outer disk of $Rgtrsim$,9,kpc exhibits a strong flare in stellar age distribution.
Stellar spectral classification is a fundamental tool of modern astronomy, providing insight into physical characteristics such as effective temperature, surface gravity, and metallicity. Accurate and fast spectral typing is an integral need for large all-sky spectroscopic surveys like the SDSS and LAMOST. Here, we present the next version of PyHammer, stellar spectral classification software that uses optical spectral templates and spectral line index measurements. PyHammer v2.0 extends the classification power to include carbon (C) stars, DA white dwarf (WD) stars, and also double-lined spectroscopic binaries (SB2). This release also includes a new empirical library of luminosity-normalized spectra that can be used to flux calibrate observed spectra, or to create synthetic SB2 spectra. We have generated physically reasonable SB2 combinations as templates, adding to PyHammer the ability to spectrally type SB2s. We test classification success rates on SB2 spectra, generated from the SDSS, across a wide range of spectral types and signal-to-noise ratios. Within the defined range of pairings described, more than $95%$ of SB2s are correctly classified.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
