Magnitude Of Red Clump Stars Research Articles

The age and metallicity dependence of the near-infrared magnitudes of red clump stars

ABSTRACT Red clump (RC) stars are widely used as an excellent standard candle. To make them even better, it is important to know the dependence of their absolute magnitudes on age and metallicity. We observed star clusters in the Large Magellanic Cloud to fill age and metallicity parameter space, which previous work has not observationally studied. We obtained the empirical relations of the age and metallicity dependence of absolute magnitudes MJ, MH, and $M_{K_{S}}$, and colours J − H, J − KS, and H − KS of RC stars, although the coefficients have large errors. Mean near-infrared magnitudes of the RC stars in the clusters show relatively strong dependence on age for young RC stars. The J − KS and H − KS colours show the nearly constant values of 0.528 ± 0.015 and 0.047 ± 0.011, respectively, at least within the ages of 1.1–3.2 Gyr and [Fe/H] of −0.90 to −0.40 dex. We also confirmed that the population effects of observational data are in good agreement with the model prediction.

Red clump stars from the LAMOST data I: identification and distance

We present a sample of about 120 000 red clump candidates selected from the LAMOST DR2 catalog based on the empirical distribution model in the effective temperature vs. surface gravity plane. Although, in general, red clump stars are considered as standard candles, they do not exactly stay in a narrow range of absolute magnitude, but may have a range of more than one magnitude depending on their initial mass. Consequently, conventional oversimplified distance estimations with the assumption of a fixed luminosity may lead to systematic bias related to the initial mass or age, which can potentially affect the study of the evolution of the Galaxy with red clump stars. We therefore employ an isochrone-based method to estimate the absolute magnitude of red clump stars from their observed surface gravities, effective temperatures and metallicities. We verify that the estimation removes the systematics well and provides initial mass/age estimates that are independent of distance with accuracy better than 10%.

Structure of the Large Magellanic Cloud from near infrared magnitudes of red clump stars

The structural parameters, like the inclination, i and the position angle of the line of nodes (PA_lon) of the disk of the Large Magellanic Cloud (LMC) are estimated using the JH photometric data of red clump stars from the Infrared Survey Facility - Magellanic Cloud Point Source Catalog (IRSF-MCPSC). The observed LMC region is divided into several sub-regions and stars in each region are cross identified with the optically identified red clump stars to obtain the near infrared magnitudes. The peak values of H magnitude and (J-H) colour of the observed red clump distribution are obtained by fitting a profile to the distributions and also by taking the average value of magnitude and colour of the red clump stars in the bin with largest number. Then the dereddened peak H0 magnitude of the red clump stars in each sub-region is obtained. The RA, Dec and relative distance from the center of each sub-region are converted into x, y & z Cartesian coordinates. A weighted least square plane fitting method is applied to this x,y,z data to estimate the structural parameters of the LMC disk. A reddening map based on (J-H) colour of the RC stars is presented. When the peaks of the red clump distribution were identified by averaging, an inclination of 25.7 +/- 1.6 and PA_lon = 141.5 +/- 4.5 were obtained. We estimate a distance modulus of 18.47 +/- 0.1 mag to the LMC. Extra-planar features which are in front as well as behind the fitted plane are identified which match with the optically identified extra-planar features. The bar of the LMC is found to be part of the disk within 500 pc. The estimates of the structural parameters are found to be independent of the photometric bands used for the analysis. We find that the inner disk, within 3.0, is less inclined and has larger value of PA_lon when compared to the outer disk.

Luminosity–colour relations for red clump stars

We calibrated the $M_V$, $M_J$, $M_{K_s}$ and $M_g$ absolute magnitudes of red clump stars in terms of colours. $M_V$ and $M_g$ are strongly dependent on colour, while the dependence of $M_J$ and $M_{K_s}$ on colour is rather weak. The calibration of $M_V$ and $M_{K_s}$ absolute magnitudes is tested on 101 RC stars in the field SA 141. The Galactic model parameters estimated with this sample are in good agreement with earlier studies.

THE ARAUCARIA PROJECT. POPULATION EFFECTS ON THEV- ANDI-BAND MAGNITUDES OF RED CLUMP STARS

We present measurements of the V and I band magnitudes of red clump stars in 15 nearby galaxies obtained from recently published homogenous HST photometry. Supplementing these results with similar data for another 8 galaxies available in the literature the populational effects on the V and I band magnitudes of red clump stars were investigated. Comparing red clump magnitudes with the I-band magnitude of the TRGB in a total sample of 23 galaxies possessing very different environments we demonstrate that population effects strongly affect both the V and I band magnitude of red clump stars in a complex way. Our empirical results basically confirm the theoretical results of Girardi and Salaris, and show that optical (VI) photometry of red clump stars is not an accurate method for the determination of distances to nearby galaxies at the present moment, as long as the population effects are not better calibrated, both empirically and theoretically. Near infrared photometry is a much better way to measure galaxy distances with red clump stars given its smaller sensitivity to population effects.

The red clump absolute magnitude based on revised Hipparcos parallaxes

Over the past decade the use of the red clump (RC) as distance indicator has increased in importance as this evolutionary phase is well populated and a good local calibration exists. The absolute calibration of the RC in the $I$ and $K$ band is investigated again based on the recently published revised Hipparcos parallaxes. A numerical model is developed that takes the various selection criteria and the properties of the Hipparcos catalogue into account. The biases involved in applying certain selections are estimated with this model. The absolute magnitudes that are found are $M_{\rm I} = -0.22 \pm 0.03$ and $M_{\rm K} = -1.54 \pm 0.04$ (on the 2MASS system). The $I$-band value is in good agreement with previous determinations, the $K$-band value is fainter than previously quoted, and this seems to be related to a selection bias whereby accurate $K$-magnitudes are only available for relatively few bright stars. Applying population corrections to the absolute $K$ magnitude of RC stars in clusters supports the fainter magnitude scale.

The old anticentre open cluster Berkeley 32: membership and fundamental parameters

We have obtained medium-low resolution spectroscopy and BV I CCD imaging of Berkeley 32, an old open cluster which lies in the anticentre direc tion. From the radial velocities of 48 stars in the cluster direction we found that 31 of them, in crucial evolutionary phases, are probable cluster members, with an average radial velocity of +106.7 (� = 8.5) km s 1 . From isochrone fitting to the colour magnitude diagrams of Be rkeley 32 we have obtained an age of 6.3 Gyr, (m − M)0= 12.48 and E(B − V ) = 0.10. The best fit is obtained with Z=0.008. A consistent distance, (m − M)0 ≃ 12.6 ± 0.1, has been derived from the mean magnitude of red clump stars with confirmed membership; we ma y assume (m − M)0 ≃ 12.55 ± 0.1 The colour magnitude diagram of the nearby field observed to c heck for field stars contamination looks intriguingly similar to that of the Canis Major overdensity.

The Araucaria Project: Dependence of MeanK,J, andIAbsolute Magnitudes of Red Clump Stars on Metallicity and Age

As a part of our ongoing Araucaria Project on the improvement of stellar distance indicators we present deep near-infrared JK imaging of several fields in four Local Group galaxies: LMC, SMC, and the Carina and Fornax dwarf galaxies. These data were obtained under excellent seeing conditions at the European Southern Observatory Very Large Telescope and New Technology Telescope. We determine the mean red clump star magnitudes in the J and K bands in the four galaxies. A comparison of the extinction-corrected K-band red clump star magnitudes with the tip of the red giant branch magnitude, the mean RR Lyrae star V-band magnitude, and the mean K-band magnitude of Cepheid variables at a period of 10 days (for the LMC and SMC) strongly suggests that the red clump star absolute K-band magnitude has a very low (if any) dependence on metallicity over the broad range of metallicities covered by our target galaxies. This finding is in contrast to the mean I- and J-band red clump star magnitudes, which do have a clear metallicity dependence and which we calibrate from our data. Excellent agreement with the former calibration of the red clump I-band magnitude dependence on metallicity of Udalski is found from our new data. We use the Galactic cluster K-band red clump star data of Grocholski & Sarajedini to demonstrate that the K-band red clump star absolute magnitude also has very little (if any) dependence on age over an age range of about 2–8 Gyr. The present study therefore provides clear evidence that the mean K-band magnitude of red clump stars is an excellent distance indicator, with very small (if any) population corrections to be applied over a large range in metallicity and age. Our findings imply that present-day population corrections calculated from models are only accurate at a ±0.15 mag level, which is a great achievement in itself but not accurate enough for high-precision distance scale work. We determine the distances to all our target galaxies from the K-band red clump magnitude, with very small statistical uncertainties. Comparing these distances with those coming from the observed mean I-band magnitudes of the red clump stars, we find evidence that there is likely to be a problem in the photometric calibration of the local, solar neighborhood red clump star K- or I-band magnitudes, which amounts to some 0.2 mag. A redetermination of the absolute photometric calibration of the Hipparcos-observed nearby red clump stars seems necessary to resolve this problem and put the derivation of absolute distances to Local Group galaxies from their red clump stars on a firmer basis.

Galactocentric Distance with the OGLE and [ITAL]Hipparcos[/ITAL] Red Clump Stars

We compare red clump stars with parallaxes known to better than 10% in the Hipparcos catalog and corrected for the interstellar extinction, with the OGLE red clump stars in Baade's Window also corrected for the interstellar extinction. There are $\sim 600$ and $\sim 10,000$ such stars in the two data sets, respectively. We find empirically that the average I-band magnitude of red clump stars does not depend on their intrinsic color in the range $ 0.8 < (V-I)_0 < 1.4 $. The red clump luminosity function is well represented by a gaussian with the peak at $ M_{I_0,m} = -0.26 $, and the dispersion $ \sigma _{RC} \approx 0.2 $ mag. This allows a single step determination of the distance to the galactic center and gives $ R_0 = 8.4 \pm 0.4 $ kpc. The number of red clump stars is so large that a formal statistical error is only $\sim 1%$. The local stars are relatively blue and have a small color dispersion: $ = 1.01, \sigma_{(V-I)} = 0.08$, while for the bulge stars $ = 1.22, \sigma_{(V-I)_0} = 0.14$. Presumably, the bulge population has a broader range and a higher average metallicity than the local disk population.

Modelling the Galactic Bar using Red Clump Stars

AbstractThe color-magnitude diagrams of ~ 1 × 106 stars obtained for 19 fields towards the Galactic bulge with the OGLE project reveal a well-defined population of bulge red clump stars. We found that the distributions of the extinction-adjusted apparent magnitudes of red clump stars in fields lying at ι = ±5° in galactic longitude differ by ∼ 0.4 mag. A plausible explanation of this observed difference in the luminosity distribution is that the Galactic bulge is a triaxial structure, or a bar, which is inclined to the line of sight by no more than 45°. The part of the bar at the positive galactic longitude is closer to us. Work is now under way to model the Galactic bar by fitting the observed luminosity functions in the red clump region for various fields. Preliminary results indicate that the angle of the inclination of the bar to the line of sight can be as small as ∼ 20°. Gravitational microlensing can provide us with additional constraints on the structure of the Galactic bar.