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Register a new userThe Distance to the Galactic Center Derived From Infrared Photometry of Bulge Red Clump Stars
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On the basis of the near infrared observations of bulge red clump stars near the Galactic center, we have determined the galactocentric distance to be R_0 = 7.52 +- 0.10 (stat) +- 0.35 (sys) kpc. We observed the red clump stars at |l| < 1.0 deg and 0.7 deg < |b| < 1.0 deg with the IRSF 1.4 m telescope and the SIRIUS camera in the H and Ks bands. After extinction and population corrections, we obtained (m - M)_0 = 14.38 +- 0.03 (stat) +- 0.10 (sys). The statistical error is dominated by the uncertainty of the intrinsic local red clump stars luminosity. The systematic error is estimated to be +- 0.10 including uncertainties in extinction and population correction, zero-point of photometry, and the fitting of the luminosity function of the red clump stars. Our result, R_0 = 7.52 kpc, is in excellent agreement with the distance determined geometrically with the star orbiting the massive black hole in the Galactic center. The recent result based on the spatial distribution of globular clusters is also consistent with our result. In addition, our study exhibits that the distance determination to the Galactic center with the red clump stars, even if the error of the population correction is taken into account, can achieve an uncertainty of about 5%, which is almost the same level as that in recent geometrical determinations.
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We propose a new way to search for hypervelocity stars in the Galactic bulge, by using red clump (RC) giants, that are good distance indicators. The 2nd Gaia Data Release and the near-IR data from the VISTA Variables in the Via Lactea (VVV) Survey led to the selection of a volume limited sample of 34 bulge RC stars. A search in this combined data set leads to the discovery of seven candidate hypervelocity red clump stars in the Milky Way bulge. Based on this search we estimate the total production rate of hypervelocity RC stars from the central supermassive black hole (SMBH) to be $N_{HVRC} = 3.26 times 10^{-4} $ yr$^{-1}$. This opens up the possibility of finding larger samples of hypervelocity stars in the Galactic bulge using future surveys, closer to their main production site, if they are originated by interactions of binaries with the central SMBH.
I determine a distance to the Fornax dwarf galaxy using stars in the red clump and at the tip of the red giant branch. They are in very good agreement, with $mu_0 = 20.66 mag$. Comparing the magnitudes of the tip of the red giant branch and of the red clump in Fornax, Carina and the Magellanic Clouds, I propose a possible solution to the problem of the discrepancy between these two types of distance measurements.
We have used the AAOMEGA spectrograph to obtain R $sim 1500$ spectra of 714 stars that are members of two red clumps in the Plaut Window Galactic bulge field $(l,b)=0^{circ},-8^{circ}$. We discern no difference between the clump populations based on radial velocities or abundances measured from the Mg$b$ index. The velocity dispersion has a strong trend with Mg$b$-index metallicity, in the sense of a declining velocity dispersion at higher metallicity. We also find a strong trend in mean radial velocity with abundance. Our red clump sample shows distinctly different kinematics for stars with [Fe/H] $<-1$, which may plausibly be attributable to a minority classical bulge or inner halo population. The transition between the two groups is smooth. The chemo-dynamical properties of our sample are reminiscent of those of the Milky Way globular cluster system. If correct, this argues for no bulge/halo dichotomy and a relatively rapid star formation history. Large surveys of the composition and kinematics of the bulge clump and red giant branch are needed to define further these trends.
We present chemical abundances in K and M red-giant members of the Galactic bulge derived from high-resolution infrared spectra obtained with the Phoenix spectrograph on Gemini-South. The elements studied are carbon, nitrogen, oxygen, sodium, titanium, and iron. The evolution of C and N abundances in the studied red-giants show that their oxygen abundances represent the original values with which the stars were born. Oxygen is a superior element for probing the timescale of bulge chemical enrichment via [O/Fe] versus [Fe/H]. The [O/Fe]-[Fe/H] relation in the bulge does not follow the disk relation, with [O/Fe] values falling above those of the disk. Titanium also behaves similarly to oxygen with respect to iron. Based on these elevated values of [O/Fe] and [Ti/Fe] extending to large Fe abundances, it is suggested that the bulge underwent a more rapid chemical enrichment than the halo. In addition, there are declines in both [O/Fe] and [Ti/Fe] in those bulge targets with the largest Fe abundances, signifying another source affecting chemical evolution: perhaps Supernovae of Type Ia. Sodium abundances increase dramatically in the bulge with increasing metallicity, possibly reflecting the metallicity dependant yields from supernovae of Type II, although Na contamination from H-burning in intermediate mass stars cannot be ruled out.
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