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Register a new userStatistical relations between stellar spectral and luminosity classes and stellar effective temperature and surface gravity
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We have determined new statistical relations to estimate the fundamental atmospheric parameters of effective temperature and surface gravity, using MK spectral classification, and vice versa. The relations were constructed based on the published calibration tables (for main sequence stars) and observational data from stellar spectral atlases (for giants and supergiants). These new relations were applied to field giants with known atmospheric parameters, and the results of the comparison of our estimations with available spectral classification had been quite satisfactory.
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Surface gravity is one of a stars basic properties, but it is difficult to measure accurately, with typical uncertainties of 25-50 per cent if measured spectroscopically and 90-150 per cent photometrically. Asteroseismology measures gravity with an uncertainty of about two per cent but is restricted to relatively small samples of bright stars, most of which are giants. The availability of high-precision measurements of brightness variations for >150,000 stars provides an opportunity to investigate whether the variations can be used to determine surface gravities. The Fourier power of granulation on a stars surface correlates physically with surface gravity; if brightness variations on timescales of hours arise from granulation, then such variations should correlate with surface gravity. Here we report an analysis of archival data that reveals an observational correlation between surface gravity and the root-mean-square brightness variations on timescales of less than eight hours for stars with temperatures of 4500-6750K, log of surface gravities of 2.5-4.5 (cgs units), and having overall brightness variations <3 parts per thousand. A straightforward observation of optical brightness variations therefore allows a determination of the surface gravity with a precision of <25 percent for inactive Sun-like stars at main-sequence to giant stages of evolution.
X-ray luminosity ($L_X$) originating from high-mass X-ray binaries (HMXBs) is tightly correlated with the host galaxys star-formation rate (SFR). We explore this connection at sub-galactic scales spanning ${sim}$7 dex in SFR and ${sim}$8 dex in specific SFR (sSFR). There is good agreement with established relations down to ${rm SFR {simeq} 10^{-3},M_odot , yr^{-1}}$, below which an excess of X-ray luminosity emerges. This excess likely arises from low mass X-ray binaries. The intrinsic scatter of the $L_X$-SFR relation is constant, not correlated with SFR. Different star formation indicators scale with $L_X$ in different ways, and we attribute the differences to the effect of star formation history. The SFR derived from H$alpha$ shows the tightest correlation with X-ray luminosity because H$alpha$ emission probes stellar populations with ages similar to HMXB formation timescales, but the H$alpha$-based SFR is reliable only for $rm sSFR{>}10^{-12},M_odot , yr^{-1}/M_odot$.
In Bastien et al. (2013) we found that high quality light curves, such as those obtained by Kepler, may be used to measure stellar surface gravity via granulation-driven light curve flicker. Here, we update and extend the relation originally presented in Bastien et al. (2013) after calibrating flicker against a more robust set of asteroseismically derived surface gravities. We describe in detail how we extract the flicker signal from the light curves, including how we treat phenomena, such as exoplanet transits and shot noise, that adversely affect the measurement of flicker. We examine the limitations of the technique, and, as a result, we now provide an updated treatment of the flicker-based logg error. We briefly highlight further applications of the technique, such as astrodensity profiling or its use in other types of stars with convective outer layers. We discuss potential uses in current and upcoming space-based photometric missions. Finally, we supply flicker-based logg values, and their uncertainties, for 27 628 Kepler stars not identified as transiting-planet hosts, with 4500<teff<7150 K, 2.5<logg<4.6, Kepler magnitude <13.5, and overall photometric amplitudes <10 parts per thousand.
We present a simultaneous analysis of galaxy cluster scaling relations between weak-lensing mass and multiple cluster observables, across a wide range of wavelengths, that probe both gas and stellar content. Our new hierarchical Bayesian model simultaneously considers the selection variable alongside all other observables in order to explicitly model intrinsic property covariance and account for selection effects. We apply this method to a sample of 41 clusters at $0.15<z<0.30$, with a well-defined selection criteria based on RASS X-ray luminosity, and observations from Chandra / XMM, SZA, Planck, UKIRT, SDSS and Subaru. These clusters have well-constrained weak-lensing mass measurements based on Subaru / Suprime-Cam observations, which serve as the reference masses in our model. We present 30 scaling relation parameters for 10 properties. All relations probing the intracluster gas are slightly shallower than self-similar predictions, in moderate tension with prior measurements, and the stellar fraction decreases with mass. K-band luminosity has the lowest intrinsic scatter with a 95th percentile of 0.16, while the lowest scatter gas probe is gas mass with a fractional intrinsic scatter of $0.16 pm 0.03$. We find no distinction between the core-excised X-ray or high-resolution Sunyaev-Zeldovich relations of clusters of different central entropy, but find with modest significance that higher entropy clusters have higher stellar fractions than their lower entropy counterparts. We also report posterior mass estimates from our likelihood model.
We investigate the scaling relations between the X-ray and the thermal Sunyaev-Zeldovich Effect (SZE) properties of clusters of galaxies, using data taken during 2007 by the Y.T. Lee Array for Microwave Background Anisotropy (AMiBA) at 94 GHz for the six clusters A1689, A1995, A2142, A2163, A2261, and A2390. The scaling relations relate the integrated Compton-y parameter Y_{2500} to the X-ray derived gas temperature T_{e}, total mass M_{2500}, and bolometric luminosity L_X within r_{2500}. Our results for the power-law index and normalization are both consistent with the self-similar model and other studies in the literature except for the Y_{2500}-L_X relation, for which a physical explanation is given though further investigation may be still needed. Our results not only provide confidence for the AMiBA project but also support our understanding of galaxy clusters.
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