arXiv subjects

J. V. Clausen

Publications and source records attributed to J. V. Clausen.

21 records · Page 2Linked to original sources

arXiv2003

Eclipsing binaries in the Magellanic Clouds. uvby CCD light curves and photometric analyses for HV982 (LMC), HV12578 (LMC), HV1433 (SMC), and HV11284 (SMC)

We present new accurate CCD uvby light curves for the LMC eclipsing binaries HV982 and HV12578, and for the SMC systems HV1433 and HV11284 obtained at the Danish 1.5m telescope at ESO, La Silla. The light curves were derived from DoPHOT photometry, and typical accuracies are between 0.007 and 0.012 mag per point. Standard uvby indices have also been established for each binary, primarily for determination of interstellar reddening and absorption. For HV982 and HV12578, accurate photometric elements have been established. Both systems consist of two detached components of comparable sizes in an eccentric orbit. Adopting the spectroscopic elements given by Fitzpatrick et al. 2002 for HV982, we derive absolute dimensions of its components which agree well with their results. A distance modulus of V_0-M_V = 18.63 +/- 0.08 is obtained, corresponding to a distance of 52.6 +/- 2.0 kpc, which is in formal agreement with (although slightly larger than) their determination. HV1433 and HV11284 both consist of two rather close, deformed and quite different stars. As the mass ratios between the components (and their rotation rates) are not known, definitive photometric elements can not yet be obtained, but we present a sample of possible photometric solutions. In a series of forthcoming papers we will combine our uvby observations with high-dispersion spectra from the UVES spectrograph on the ESO Very Large Telescope (VLT) and present absolute dimensions, chemical abundances and distances for selected LMC and SMC systems, including HV12578 and refined results for HV982.

astro-ph↗

arXiv2002

The CORALIE survey for southern extra-solar planets IX. A 1.3-day period brown dwarf disguised as a planet

In this article we present the case of HD 41004 AB, a system composed of a K0V star and a 3.7-magnitude fainter M-dwarf companion separated by only 0.5 arcsec. An analysis of CORALIE radial-velocity measurements has revealed a variation with an amplitude of about 50m/s and a periodicity of 1.3days. This radial-velocity signal is consistent with the expected variation induced by the presence a very low mass giant planetary companion to HD 41004 A, whose light dominates the spectra. The radial-velocity measurements were then complemented with a photometric campaign and with the analysis of the bisector of the CORALIE Cross-Correlation Function (CCF). While the former revealed no significant variations within the observational precision of 0.003-0.004 mag (except for an observed flare event), the bisector analysis showed that the line profiles are varying in phase with the radial-velocity. This latter result, complemented with a series of simulations, has shown that we can explain the observations by considering that HD 41004 B has a brown-dwarf companion orbiting with the observed 1.3-day period. If confirmed, this detection represents the first discovery of a brown dwarf in a very short period (1.3-day) orbit around an M dwarf. Finally, this case should be taken as a serious warning about the importance of analyzing the bisector when looking for planets using radial-velocity techniques.

astro-ph↗

arXiv2000

Reddenings and metallicities in the LMC and SMC from Stroemgren CCD photometry

The individual reddenings for B stars in two fields in the Small Magellanic Cloud (SMC) and two fields in the Large Magellanic Cloud (LMC) are determined by means of Stroemgren uvby CCD photometry. In both LMC fields we find a foreground reddening of E(B-V) = 0.085 +/- 0.02, and for the SMC fields we find E(B-V) = 0.070 +/- 0.02. In addition to the foreground reddening we find contributions from reddening intrinsically in the Clouds up to E(B-V) ~ 0.21. The intrinsic contribution is not correlated with position within our 6 x 4.5 arcmin CCD fields but varies in an essentially random way. Unless the reddening is measured for a particular object, it will be uncertain by +/- 0.035 in E(B-V) (best case, far from the central bars) to more than +/- 0.10 (close to the central bars). The Stroemgren vby photometry has been used to derive metallicities for GK giant stars in the observed fields. Adopting average reddenings we obtain mean metallicities which are consistent with those found from spectroscopic studies of F and G supergiants but with a considerable scatter, from [Fe/H]~ -2.0 to > 0. A significant fraction of the scatter is, however, due to reddening variations rather than being intrinsic. The possible existence of high metallicity stars should be investigated further using spectroscopic methods.

astro-ph↗