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Register a new userFrom the Inner to Outer Milky Way: A Photometric Sample of 2.6 Million Red Clump Stars
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Large pristine samples of red clump stars are highly sought after given that they are standard candles and give precise distances even at large distances. However, it is difficult to cleanly select red clumps stars because they can have the same T$_{mathrm{eff}}$ and log $g$ as red giant branch stars. Recently, it was shown that the asteroseismic parameters, $rm{Delta}$P and $rm{Delta u}$, which are used to accurately select red clump stars, can be derived from spectra using the change in the surface carbon to nitrogen ratio ([C/N]) caused by mixing during the red giant branch. This change in [C/N] can also impact the spectral energy distribution. In this study, we predict the $rm{Delta}$P, $rm{Delta u}$, T$_{mathrm{eff}}$ and log $g$ using 2MASS, AllWISE, gaia, and Pan-STARRS data in order to select a clean sample of red clump stars. We achieve a contamination rate of $sim$20%, equivalent to what is achieved when selecting from T$_{mathrm{eff}}$ and log $g$ derived from low resolution spectra. Finally, we present two red clump samples. One sample has a contamination rate of $sim$ 20% and $sim$ 405,000 red clump stars. The other has a contamination of $sim$ 33% and $sim$ 2.6 million red clump stars which includes $sim$ 75,000 stars at distances $>$ 10 kpc. For |b|>30 degrees we find $sim$ 15,000 stars with contamination rate of $sim$ 9%. The scientific potential of this catalog for studying the structure and formation history of the Galaxy is vast given that it includes millions of precise distances to stars in the inner bulge and distant halo where astrometric distances are imprecise.
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The Hipparcos orbiting observatory has revealed a large number of helium-core-burning clump stars in the Galactic field. These low-mass stars exhibit signatures of extra-mixing processes that require modeling beyond the first dredge-up of standard models. The 12C/13C ratio is the most robust diagnostic of deep mixing, because it is insensitive to the adopted stellar parameters. In this work we present 12C/13C determinations in a sample of 34 Galactic clump stars as well as abundances of nitrogen, carbon and oxygen. Abundances of carbon were studied using the C2 Swan (0,1) band head at 5635.5 A. The wavelength interval 7980-8130 A with strong CN features was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 A. Compared with the Sun and dwarf stars of the Galactic disk, mean abundances in the investigated clump stars suggest that carbon is depleted by about 0.2 dex, nitrogen is enhanced by 0.2 dex and oxygen is close to abundances in dwarfs. Comparisons to evolutionary models show that the stars fall into two groups: the one is of first ascent giants with carbon isotope ratios altered according to the first dredge-up prediction, and the other one is of helium-core-burning stars with carbon isotope ratios altered by extra mixing. The stars investigated fall to these groups in approximately equal numbers.
I review the literature covering the issue of interstellar extinction toward the Milky Way bulge, with emphasis placed on findings from planetary nebulae, RR Lyrae, and red clump stars. I also report on observations from HI gas and globular clusters. I show that there has been substantial progress in this field in recent decades, most particularly from red clump stars. The spatial coverage of extinction maps has increased by a factor $sim 100 times$ in the past twenty years, and the total-to-selective extinction ratios reported have shifted by $sim$20-25%, indicative of the improved accuracy and separately, of a steeper-than-standard extinction curve. Problems remain in modelling differential extinction, explaining anomalies involving the planetary nebulae, and understanding the difference between bulge extinction coefficients and standard literature values.
We present a sample of $sim$ 140,000 primary red clump (RC) stars of spectral signal-to-noise ratios higher than 20 from the LAMOST Galactic spectroscopic surveys, selected based on their positions in the metallicity-dependent effective temperature--surface gravity and color--metallicity diagrams, supervised by high-quality $Kepler$ asteroseismology data. The stellar masses and ages of those stars are further determined from the LAMOST spectra, using the Kernel Principal Component Analysis method, trained with thousands of RCs in the LAMOST-$Kepler$ fields with accurate asteroseismic mass measurements. The purity and completeness of our primary RC sample are generally higher than 80 per cent. For the mass and age, a variety of tests show typical uncertainties of 15 and 30 per cent, respectively. Using over ten thousand primary RCs with accurate distance measurements from the parallaxes of Gaia DR2, we re-calibrate the $K_{rm s}$ absolute magnitudes of primary RCs by, for the first time, considering both the metallicity and age dependencies. With the the new calibration, distances are derived for all the primary RCs, with a typical uncertainty of 5--10 per cent, even better than the values yielded by the Gaia parallax measurements for stars beyond 3--4 kpc. The sample covers a significant volume of the Galactic disk of $4 leq R leq 16$ kpc, $|Z| leq 5$ kpc, and $-20 leq phi leq 50^{circ}$. Stellar atmospheric parameters, line-of-sight velocities and elemental abundances derived from the LAMOST spectra and proper motions of Gaia DR2 are also provided for the sample stars. Finally, the selection function of the sample is carefully evaluated in the color-magnitude plane for different sky areas. The sample is publicly available.
We present a comprehensive study of the chemical properties of the stellar haloes of Milky-Way mass galaxies, analysing the transition between the inner to the outer haloes. We find the transition radius between the relative dominance of the inner-halo and outer-halo stellar populations to be ~15-20 kpc for most of our haloes, similar to that inferred for the Milky Way from recent observations. While the number density of stars in the simulated inner-halo populations decreases rapidly with distance, the outer-halo populations contribute about 20-40 per cent in the fiducial solar neighborhood, in particular at the lowest metallicities. We have determined [Fe/H] profiles for our simulated haloes; they exhibit flat or mild gradients, in the range [-0.002, -0.01 ] dex/kpc. The metallicity distribution functions exhibit different features, reflecting the different assembly history of the individual stellar haloes. We find that stellar haloes formed with larger contributions from massive subgalactic systems have steeper metallicity gradients. Very metal-poor stars are mainly contributed to the halo systems by lower-mass satellites. There is a clear trend among the predicted metallicity distribution functions that a higher fraction of low-metallicity stars are found with increasing radius. These properties are consistent with the range of behaviours observed for stellar haloes of nearby galaxies.
Red clump stars (RCs) are useful tracers of distances, extinction, chemical abundances, and Galactic structures and kinematics. Accurate estimation of the RC parameters -- absolute magnitude and intrinsic color -- is the basis for obtaining high-precision RC distances. By combining astrometric data from Gaia, spectroscopic data from APOGEE and LAMOST, and multi-band photometric data from Gaia, APASS, Pan-STARRS1, 2MASS, and WISE surveys, we use the Gaussian process regression to train machine learners to derive the multi-band absolute magnitudes $M_lambda$ and intrinsic colors $(lambda_1-lambda_2)_0$ for each spectral RC. The dependence of $M_lambda$ on metallicity decreases from optical to infrared bands, while the dependence of $M_lambda$ on age is relatively similar in each band. $(lambda_1-lambda_2)_0$ are more affected by metallicity than age. The RC parameters are not suitable to be represented by simple constants but are related to the Galactic stellar population structure. By analyzing the variation of $M_lambda$ and $(lambda_1-lambda_2)_0$ in the spatial distribution, we construct $(R, z)$ dependent maps of mean absolute magnitudes and mean intrinsic colors of the Galactic RCs. Through external and internal validation, we find that using three-dimensional (3D) parameter maps to determine RC parameters avoids systematic bias and reduces dispersion by about 20% compared to using constant parameters. Based on Gaias EDR3 parallax, our 3D parameter maps, and extinction-distance profile selection, we obtain a photometric RC sample containing 11 million stars with distance and extinction measurements.
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