Determining the Absolute Magnitudes of Galactic-Bulge Red Clump Giants in the Z and Y Filters of the Vista Sky Surveys and the IRAC Filters of the Spitzer Sky Surveys

Abstract

The properties of red clump giants in the central regions of the Galactic bulge are investigated in the photometric Z and Y bands of the infrared VVV (VISTA/ESO) survey and the [3.6], [4.5], [5.8], and [8.0] bands of the GLIMPSE (Spitzer/IRAC) Galactic plane survey. The absolute magnitudes for objects of this class have been determined in these bands for the first time:A comparison of the measured magnitudes with the predictions of theoretical models for the spectra of the objects under study has demonstrated good mutual agreement and has allowed some important constraints to be obtained for the properties of bulge red clump giants. In particular, a comparison with evolutionary tracks has shown that we are dealing predominantly with the high-metallicity subgroup of bulge red clump giants. Their metallicity is slightly higher than has been thought previously, [M/H] 0.40 (Z 0.038) with an error of [M/H] 0.1 dex, while the effective temperature is 4250 ± 150 K. Stars with an age of 9-10 Gyr are shown to dominate among the red clump giants, although some number of younger objects with an age of ∼ 8 can also be present. In addition, the distances to several Galactic bulge regions have been measured, as D = 8200-8500 pc, and the extinction law in these directions is shown to differ noticeably from the standard one.

GRO J1750–27: A neutron star far behind the Galactic Center switching into the propeller regime

“…This, of course, requires a knowledge of an extinction law in the direction to the source. It is especially important, taking into account preliminary estimates of the distance to GRO J1750−27 as > 12 kpc (Scott et al 1997;Shaw et al 2009) and a number of previous publications, where it was shown that the extinction law for the central regions of the Galaxy might significantly differ from the standard one (see, e.g., Nishiyama et al 2009;Revnivtsev et al 2010;Karasev et al 2010Karasev et al , 2015Alonso-García et al 2017;Karasev & Lutovinov 2018). For the following analysis we used the absorption law and extinction ratios in different filters, obtained by Alonso-García et al (2017) from the VVV survey data for the Galactic Center direction.…”

“…The observed magnitude and color of the centroid of red clump giants (RCG) are mKs,RCG = 13.85 ± 0.05 and (H − Ks) ′ = 0.84 ± 0.04, respectively. Knowing an absolute magnitude and unabsorbed color of RCGs in these filters MKs,RCG = −1.61 ± 0.03 and (H − Ks)0 = 0.11 ± 0.03 (Alves 2000;Gontcharov 2017;Karasev & Lutovinov 2018), we can determine the absorption magnitude to RCGs (and subsequently to the Galactic bulge) as AKs = 0.83 ± 0.06 based on the relation AH − AKs = (H − Ks) ′ − (H − Ks)0 and the extinction ratio from Alonso-García et al (2017). It is known that the distance to RCGs (or in other world to the bar) can vary at different longitudes (see, e.g., Gerhard & Martinez-Valpuesta 2012).…”

Optical Identification of X-ray Sources from the 14-Year INTEGRAL All-Sky Survey

“…lower than that at its center. We then compare the observed RCG color with the true RCG color, which is ([3.6] − [4.5]) 0 = −0.10 ± 0.02 (Karasev et al 2018) for the bulge, and, as a result, we obtain the sough-for reddening E([3.6] − [4.5]) bulge . However, when investigating the color-apparent magnitude diagram constructed for mid-infrared filters, it is very difficult to determine the RCG position on it directly (by investigating the local density of objects on the diagram and the broadening of the giant branch).…”

“…Moreover, RCGs are usually located at magnitudes close to the detection limits of the corresponding surveys. To solve this problem, we use the approach applied in Karasev et al (2018): first we find RCGs on the diagrams constructed for all star-like objects of the sky region being investigated in near-infrared filters (for example, Ks(J -Ks)) from the VVV or UKIDSS data; then we find a correspondence for these RCGs in the mid-infrared. Thus, having identi-fied RCGs on the [3.6]([3.6] − [4.5]) diagram, we can determine their apparent color (Fig.…”

Properties of the transient X-ray pulsar Swift J1816.7–1613 and its optical companion

“…To obtain reliable estimates of the absorption and other parameters using this method, we need to know a correct extinction law in the direction towards the source. Here we use a nonstandard law A Ks /E(J − K s) ≈ 0.43 and obtained for the Galactic bulge interstellar medium by Karasev et al (2015a), Alonso-García et al ( 2017), and Karasev & Lutovinov (2018). It is significantly different from the standard one (Cardelli et al 1989) and more suitable for studying the central parts of the Galaxy.…”