The Origins of the Ultramassive White Dwarf GD50

Original paper can be found at: http://www.astrosociety.org/pubs/cs/361.html Copyright ASPOn the basis of astrometric and spectroscopic data we argue that the ultramassive white dwarf GD 50 is associated with the star formation event that created the Pleiades and is potentially a former cluster member. Its cooling time (∼60Myrs) is consistent with it having evolved essentially as a single star from a M > 6M⊙ progenitor so there appears to be no need to invoke a white dwarf–white dwarf binary merger scenario to account for its existence. Our result may represent the first direct observational evidence that single star evolution can produce white dwarfs with M > 1.1M⊙, as predicted by some stellar evo- lutionary theories. Additionally, our findings may help towards alleviating the difficulties in reconciling the observed number of hot nearby ultramassive white dwarfs with the smaller number predicted by binary evolution models under the assumption that they are the products of white dwarf mergers

Linear polarization of galactic center in near infrared

Copyright European Southern ObservatoryPeer reviewe

On the accretion disc properties in eclipsing dwarf nova EM Cyg

In this paper we analyzed the behavior of the unusual dwarf nova EM Cyg using the data obtained in April-October, 2007 in Vyhorlat observatory (Slovak Republic) and in September, 2006 in Crimean Astrophysical Observatory (Ukraine). During our observations EM Cyg has shown outbursts in every 15-40 days. Because on the light curves of EM Cyg the partial eclipse of an accretion disc is observed we applied the eclipse mapping technique to reconstruct the temperature distribution in eclipsed parts of the disc. Calculations of the accretion rate in the system were made for the quiescent and the outburst states of activity for different distances.Comment: 6 pages, 3 figures, accepted in Astrophysics and Space Scienc

Low Frequency Flickering of TT Arietis:Hard and Soft X-ray Emission Region

Using archival ASCA observations of TT Arietis, X-ray energy spectra and power spectra of the intensity time series are presented for the first time. The energy spectra are well-fitted by a two continuum plasma emission model with temperatures around 1 keV and 10 keV. A coherent feature at about 0.643 mHz appeared in the power spectra during the observation.Comment: 9 pages in PostScript including figures, accepted for publication in Astrophysics and Space Science, available at http://astroa.physics.metu.edu.tr/preprints.htm

The missing M dwarfs

Peer reviewe

On the origin of the ultramassive white dwarf GD 50

The definitive version is available at www.blackwell-synergy.com Copyright Blackwell Publishing DOI : 10.1111/j.1745-3933.2006.00240.xPeer reviewe

An Infrared Spectral Sequence for M Dwarfs

Original paper can be found at: http://www.astrosociety.org/pubs/cs/035-069.html--Copyright Astronomical Society of the PacificWe present a spectral sequence from 1-2.5 um of M dwarfs from GL411 which is classified as M2V to the best brown dwarf candidate GD165B (M10V). This sequence shows the progressive importance of water vapour in the stmospheres of M dwarfs. We take the strength of the water absorption bands as the basis of a new method to derive effective temperatures. We also identify many of the stronger atomic and molecular features and find that their strengths correlate with our derived temperature scale

Brown Dwarfs and low-mass stars in the Pleiades and Praesepe: membership and binarity

The definitive version is available at www.blackwell-synergy.com '.--Copyright Blackwell Publishing DOI : 10.1046/j.1365-8711.2003.06630.xWe present near infrared J-, H- and K-band photometry and optical spectroscopy of low-mass star and brown dwarf (BD) candidates in the Pleiades and Praesepe open clusters. We flag non-members from their position in K, I-K and J, J-K colour- magnitude diagrams (CMDs), and J-H, H-K two-colour diagrams.Peer reviewe

Praesepe and the seven white dwarfs

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Linear polarization measurements of Omicron-Sco in near infrared

Copyright Royal Astronomical Society [Full text of this article is not available in the UHRA]Peer reviewe