128 research outputs found
The Characteristics of Magnetic CVs in the Period Gap
We have observed several magnetic cataclysmic variables located in the range
between 2 and 3 hours, known as the period gap. This work was prompted by the
recent discovery of RX J1554.2+2721. It has 2.54 hours orbital period and shows
almost pure cyclotron continuum in a low luminosity state, similar to
HS1023+3900,
HS0922+1333 and RBS206. These are low accretion rate polars (LARPs) known to
have mass transfer rates of order of a few 10^-13Msun/year.
The aim of the study was to find out, if magnetic systems filling the period
gap are in any way different from their counterparts outside that range of
periods. The only significant difference we encounter, is much higher number of
asynchronous magnetic systems to-wards longer periods than below the gap.Comment: 7 pages, 7 figures, To appear in `Magnetic Cataclysmic Variables',
IAU Col. 190 (Cape Town), eds. M. Cropper & S. Vrielman
Multi-epoch <i>L</i>-band Spectroscopy of the Be Star μ Centauri Prior to Outburst
With the aim of contributing to the understanding of the disk formation process in Be stars, we pursued a one-year spectroscopic observing campaign of the Be star μ Centauri in the L-band, using VLT/ISAAC. We present the nine near-IR spectra we obtained in an epoch of relative photometric quiescence prior to an outburst of ΔV = 0.4 magnitude. Visual estimates during the epoch of our L-band spectroscopy are also presented for the first time, together with the unpublished complete visual light curve between the years 1998 and 2014. We observe significant and monotonic changes in emission line strength of Bracket-α and Pfund-γ lines relative to Humphreys lines, and also in the continuum slope. We interpret these observed changes in terms of important changes to the column density of the line emitting regions, moving from an optically thin to an optically thick stage just prior to a major outburst. For each observing date, we provide estimates for the column density and relative extension of the line emitting region. If the changes observed toward the end of our observing campaign were related to mass-loss changes from the central star, they would correspond to an increase in a factor of two in the mass of the disk in the innermost region. If related to the visual outburst observed one month later, the variability observed in our spectra would be the first detection of the early disk formation process in the L-band.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica
K- and L-band spectroscopy of Be stars
We describe the behaviour of IR hydrogen emission lines of a sample of Be stars and discuss the physical properties of the circumstellar envelopes of Be stars classified in Groups I and II (Mennickent et al. 2009). We find that while Humphreys and Pfund lines of Group I stars form in an optically thick envelope/disk, Group II stars show Pfund lines that form in an optically thick medium and Humphreys lines originating in optically thinner regions. The transition between Groups I and II could be understood in terms of the evolution of the circumstellar disk of the star and might bring clues on the mechanism originating the Be phenomeno
High spectral resolution time-resolved optical spectroscopy of V893 Sco
We present high resolution time-resolved optical spectra of the high
inclination short orbital period dwarf nova V893 Sco. We performed spectral
analysis through radial velocity measurements, Doppler mapping, and ratioed
Doppler maps. Our results indicate that V893 Sco's accretion disk is dissimilar
to WZ Sge's accretion disk, and does not fit any of the current accretion disk
models. We derive the system parameters M1 and i, and present evidence for V893
Sco as a very young cataclysmic variable and an ER UMa star. We advance the
hypothesis that all ER UMa stars may be newly formed cataclysmic variables.Comment: 23 pages (total), 8 figures, accepted by Ap
On the secondary star of the cataclysmic variable 1RXS J094432.1+035738
We present V and Rc band photometry and optical near-infrared spectroscopy of
the cataclysmic variable 1RXS J094432.1+035738. We detected features of a cool
secondary star, which can be modeled with a red dwarf of spectral type M2 (+0.5
-1.0) V at a distance of 433 +- 100 pc.Comment: Accepted for publication in Astronomy and Astrophysic
Spectroscopic Observations of Twenty-one Faint Cataclysmic Variables Candidates
We provide the first minimum light spectroscopic observations for 21
previously known or suspected faint cataclysmic variable candidates. The
sources were selected from the Downes et al. (2001) living edition catalog and
the identified candidates have minimum light magnitudes of V~18-22. We confirm
15 of the candidates to be cataclysmic variables.Comment: 10 pages, 4 figures, accepted by A&
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