Investigations of the Non-Linear LMC Cepheid Period-Luminosity Relation with Testimator and Schwarz Information Criterion Methods

In this paper, we investigate the linearity versus non-linearity of the Large Magellanic Cloud (LMC) Cepheid period-luminosity (P-L) relation using two statistical approaches not previously applied to this problem: the testimator method and the Schwarz Information Criterion (SIC). The testimator method is extended to multiple stages for the first time, shown to be unbiased and the variance of the estimated slope can be proved to be smaller than the standard slope estimated from linear regression theory. The Schwarz Information Criterion (also known as the Bayesian Information Criterion) is more conservative than the Akaike Information Criterion and tends to choose lower order models. By using simulated data sets, we verify that these statistical techniques can be used to detect intrinsically linear and/or non-linear P-L relations. These methods are then applied to independent LMC Cepheid data sets from the OGLE project and the MACHO project, respectively. Our results imply that there is a change of slope in longer period ranges for all of the data sets. This strongly supports previous results, obtained from independent statistical tests, that the observed LMC P-L relation is non-linear with a break period at/around 10 days.Comment: 9 pages, 5 figures and 3 tables, PASP accepte

Photometry of the Magnetic White Dwarf SDSS 121209.31+013627.7

The results of 27 hours of time series photometry of SDSS 121209.31+013627.7 are presented. The binary period established from spectroscopy is confirmed and refined to 0.061412 d (88.43 minutes). The photometric variations are dominated by a brightening of about 16 mmag, lasting a little less than half a binary cycle. The amplitude is approximately the same in V, R and white light. A secondary small brightness increase during each cycle may also be present. We speculate that SDSS 121209.31+013627.7 may be a polar in a low state.Comment: Accepted for publication in MNRA

KPD 0422+5421: A New Short Period Subdwarf B/White Dwarf Binary

The sdB star KPD 0422+5421 was discovered to be a single-lined spectroscopic binary with a period of P=0.0901795 +/- (3\times 10^{-7}) days (2 hours, 10 minutes). The U and B light curves display an ellipsoidal modulation with amplitudes of about 0.02 magnitudes. The sdB star contributes nearly all of the observed flux. This and the absence of any reflection effect suggest that the unseen companion star is small (i.e. R_comp ~ 0.01 solar radii) and therefore degenerate. We modeled the U and B light curves and derived i = 78.05 +/- 0.50 degrees and a mass ratio of q = M_comp/M_sdB = 0.87 +/- 0.15. The sdB star fills 69% of its Roche lobe. These quantities may be combined with the mass function of the companion (f(M) = 0.126 +/- 0.028 solar masses) to derive M_sdB = 0.72 +/- 0.26 solar masses and M_comp = 0.62 +/- 0.18 solar masses. We used model spectra to derive the effective temperature, surface gravity, and helium abundance of the sdB star. We found T_eff = 25,000 +/- 1500K, log g = 5.4 +/- 0.1, and [He/H] = -1.0. With a period of 2 hours and 10 minutes, KPD 0422+5421 has one of the shortest known orbital periods of a detached binary. This system is also one of only a few known binaries which contain a subdwarf B star and a white dwarf. Thus KPD 0422+5421 represents a relatively unobserved, and short-lived, stage of binary star evolution.Comment: 9 pages, 8 figures, to appear in MNRAS, LaTeX, uses mn.st

New Periodic Variables from the Hipparcos Epoch Photometry

Two selection statistics are used to extract new candidate periodic variables from the epoch photometry of the Hipparcos catalogue. The primary selection criterion is a signal to noise ratio. The dependence of this statistic on the number of observations is calibrated using about 30 000 randomly permuted Hipparcos datasets. A significance level of 0.1% is used to extract a first batch of candidate variables. The second criterion requires that the optimal frequency be unaffected if the data are de-trended by low order polynomials. We find 2675 new candidate periodic variables, of which the majority (2082) are from the Hipparcos "unsolved" variables. Potential problems with the interpretation of the data (e.g. aliasing) are discussed.Comment: 18 pages, 9 figures, accepted for publication in MNRA

Texture in thin film silicides and germanides : a review

Silicides and germanides are compounds consisting of a metal and silicon or germanium. In the microelectronics industry, silicides are the material of choice for contacting silicon based devices (over the years, CoSi2, C54-TiSi2, and NiSi have been adopted), while germanides are considered as a top candidate for contacting future germanium based electronics. Since also strain engineering through the use of Si1-xGex in the source/drain/gate regions of MOSFET devices is an important technique for improving device characteristics in modern Si-based microelectronics industry, a profound understanding of the formation of silicide/germanide contacts to silicon and germanium is of utmost importance. The crystallographic texture of these films, which is defined as the statistical distribution of the orientation of the grains in the film, has been the subject of scientific studies since the 1970s. Different types of texture like epitaxy, axiotaxy, fiber, or combinations thereof have been observed in such films. In recent years, it has become increasingly clear that film texture can have a profound influence on the formation and stability of silicide/germanide contacts, as it controls the type and orientation of grain boundaries (affecting diffusion and agglomeration) and the interface energy (affecting nucleation during the solid-state reaction). Furthermore, the texture also has an impact on the electrical characteristics of the contact, as the orientation and size of individual grains influences functional properties such as contact resistance and sheet resistance and will induce local variations in strain and Schottky barrier height. This review aims to give a comprehensive overview of the scientific work that has been published in the field of texture studies on thin film silicide/germanide contacts. Published by AIP Publishing

Oviductal and uterine leiomyomata in mares

This paper describes a case of a sessile uterine leiomyoma in a 17-year-old chronic infertile Selle Francais mare. The mass was removed by transendoscopic electrocoagulation. In the same period, 725 mares were screened for oviductal and uterine solid masses in a slaughterhouse survey. Two uterine masses and one oviductal mass were detected in three different mares. Histological and immunohistochemical examination revealed leiomyoma in the four masses. To the authors' knowledge, this is the first report of an oviductal leiomyoma in a mare

Two candidate brown dwarf companions around core helium-burning stars

Hot subdwarf stars of spectral type B (sdBs) are evolved, core helium-burning objects. The formation of those objects is puzzling, because the progenitor star has to lose almost its entire hydrogen envelope in the red-giant phase. Binary interactions have been invoked, but single sdBs exist as well. We report the discovery of two close hot subdwarf binaries with small radial velocity amplitudes. Follow-up photometry revealed reflection effects originating from cool irradiated companions, but no eclipses. The lower mass limits for the companions of CPD-64$^{\circ}$481 ($0.048\,M_{\rm \odot}$) and PHL\,457 ($0.027\,M_{\rm \odot}$) are significantly below the stellar mass limit. Hence they could be brown dwarfs unless the inclination is unfavourable. Two very similar systems have already been reported. The probability that none of them is a brown dwarf is very small, 0.02%. Hence we provide further evidence that substellar companions with masses that low are able to eject a common envelope and form an sdB star. Furthermore, we find that the properties of the observed sample of hot subdwarfs in reflection effect binaries is consistent with a scenario where single sdBs can still be formed via common envelope events, but their low-mass substellar companions do not survive.Comment: accepted to A&