325 research outputs found
The New Contact Binary GSC 2414-0797
Original article can be found at: http://www.konkoly.hu/ibvs/GSC 2414-0797 has a contact binary star type light curve, a 0.4 magnitude brightness variation with a period 0.3406 days.Peer reviewe
A search for flares and mass ejections on young late-type stars in the open cluster Blanco-1
We present a search for stellar activity (flares and mass ejections) in a
sample of 28 stars in the young open cluster Blanco-1. We use optical spectra
obtained with ESO's VIMOS multi-object spectrograph installed on the VLT. From
the total observing time of 5 hours, we find four H flares but
no distinct indication of coronal mass ejections (CMEs) on the investigated
dK-dM stars. Two flares show "dips" in their light-curves right before their
impulsive phases which are similar to previous discoveries in photometric
light-curves of active dMe stars. We estimate an upper limit of 4 CMEs per
day per star and discuss this result with respect to a semi- empirical
estimation of the CME rate of main-sequence stars. We find that we should have
detected at least one CME per star with a mass of 1-15 g
depending on the star's X-ray luminosity, but the estimated H fluxes
associated with these masses are below the detection limit of our observations.
We conclude that the parameter which mainly influences the detection of stellar
CMEs using the method of Doppler-shifted emission caused by moving plasma is
not the spectral resolution or velocity but the flux or mass of the CME.Comment: Accepted for publication in MNRAS, accepted 2014 June 10, received
2014 June 5, in original form 2014 March 24, 14 pages, 5 figure
DE Canum Venaticorum: A Bright, Eclipsing Red DwarfâWhite Dwarf Binary
Close white dwarf - red dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarf - red dwarf binary with a relatively short (~8.7 hours) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters which we discuss in the frame work of common-envelope evolution. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average low-resolution spectrum of DE CVn we constrain the temperature of the white dwarf and the spectral type of the red dwarf. The eclipse light curve is analysed and combined with the radial velocity curve of the red dwarf determined from time-resolved spectroscopy to derive constraints on the inclination and the masses of the components in the system
IPHAS and the symbiotic stars. I. Selection method and first discoveries
The study of symbiotic stars is essential to understand important aspects of
stellar evolution in interacting binaries. Their observed population in the
Galaxy is however poorly known, and is one to three orders of magnitudes
smaller than the predicted population size. IPHAS, the INT Photometric Halpha
survey of the Northern Galactic plane, gives us the opportunity to make a
systematic, complete search for symbiotic stars in a magnitude-limited volume,
and discover a significant number of new systems.
A method of selecting candidate symbiotic stars by combining IPHAS and
near-IR (2MASS) colours is presented. It allows us to distinguish symbiotic
binaries from normal stars and most of the other types of Halpha emission line
stars in the Galaxy. The only exception are T Tauri stars, which can however be
recognized because of their concentration in star forming regions. Using these
selection criteria, we discuss the classification of a list of 4338 IPHAS stars
with Halpha in emission. 1500 to 2000 of them are likely to be Be stars. Among
the remaining objects, 1183 fulfill our photometric constraints to be
considered candidate symbiotic stars. The spectroscopic confirmation of three
of these objects, which are the first new symbiotic stars discovered by IPHAS,
proves the potential of the survey and selection method.Comment: Accepted for publication on Astronomy and Astrophysics. 12 pages, 8
figure
Candidate planetary nebulae in the IPHAS photometric catalogue
Original article can be found at: http://www.aanda.org/ Copyright European Southern Observatory. DOI: 10.1051/0004-6361/200912002Context. We have carried out a semi-automated search for planetary nebulae (PNe) in the INT photometric H-alpha survey (IPHAS) catalogue. We present the PN search and the list of selected candidates. We cross correlate the selected candidates with a number of existing infrared galactic surveys in order to gain further insight into the nature of the candidates. Spectroscopy of a subset of objects is used to estimate the number of PNe present in the entire candidate list. Aims. The overall aim of the IPHAS PN project is to carry out a deep census of PNe in the northern Galactic plane, an area where PN detections are clearly lacking. Methods. The PN search is carried out on the IPHAS photometric catalogue. The candidate selection is based on the IPHAS and 2MASS/UKIDSS colours of the objects and the final candidate selection is made visually. Results. From the original list of ~600 million IPHAS detections we have selected a total of 1005 objects. Of these, 224 are known objects, leaving us with 781 PN candidates. Based on the initial follow-up spectroscopy, we expect the list to include very young and proto-PNe in addition to genuine, normal PNe (~16%) and emission line objects other than PNe. We present additional criteria to select the most probable PN candidates from our candidate list.Peer reviewe
DE Canum Venaticorum : a bright, eclipsing red dwarfâwhite dwarf binary
Context. Close white dwarfâred dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarfâred dwarf binary with a relatively short (âŒ8.7 h) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study.
Aims. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters that we discuss in the framework of common-envelope evolution.
Methods. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average lowresolution spectrum of DE CVn, we constrain the temperature of the white dwarf and the spectral type of the red dwarf. The eclipse light curve is analysed and combined with the radial velocity curve of the red dwarf determined from time-resolved spectroscopy to derive constraints on the inclination and the masses of the components in the system.
Results. The derived ephemeris is HJDmin = 2 452 784.5533(1) + 0.3641394(2) Ă E. The red dwarf in DE CVn has a spectral type of M3V and the white dwarf has an effective temperature of 8 000 K. The inclination of the system is 86+3⊠â2 and the mass and radius of the red dwarf are 0.41 ± 0.06 M and 0.37+0.06 â0.007 R, respectively, and the mass and radius of the white dwarf are 0.51+0.06
â0.02 M and 0.0136+0.0008 â0.0002 R, respectively.
Conclusions. We found that the white dwarf has a hydrogen-rich atmosphere (DA-type). Given that DE CVn has experienced a common-envelope phase, we can reconstruct its evolution and we find that the progenitor of the white dwarf was a relatively lowmass star (M †1.6 M). The current age of this system is 3.3â7.3 Ă 109 years, while it will take longer than the Hubble time for DE CVn to evolve into a semi-detached system
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