25 research outputs found
The Blazhko behaviour of RR Geminorum I - CCD photometric results in 2004
Extended CCD monitoring of RR Gem revealed that it is a Blazhko type RRab
star with the shortest Blazhko period (7.23d) and smallest modulation amplitude
(Delta Mmax<0.1 mag) currently known. The short period of the modulation cycle
enabled us to obtain complete phase coverage of the pulsation at each phase of
the modulation. This is the first multicolour observation of a Blazhko star
which is extended enough to define accurate mean magnitudes and colours of the
variable at different Blazhko phases. Small, but real, changes in the intensity
mean colours at different Blazhko phases have been detected. The Fourier
analysis of the light curves shows that, in spite of the mmag and smaller order
of the amplitudes, the triplet structure is noticeable up to about the 14th
harmonic. The modulation is concentrated to a very narrow, 0.2 phase range of
the pulsation, centred on the supposed onset of the H emission during rising
light. These observational results raise further complications for theoretical
explanation of the long known but poorly understood Blazhko phenomenon.Comment: 10 pages, 12 figures, 3 tables. Accepted for publication in Astronomy
and Astrophysic
Period changes in six semi-detached Algol-type binaries
Six semi-detached Algol-type binaries lacking a period analysis were chosen
to test for a presence of a third body. The O-C diagrams of these binaries were
analyzed with the least-squares method by using all available times of minima.
Also fourteen new minima, obtained from our observations, were included in the
present research. The light-time effect was adopted as a main factor for the
detailed description of the long-term period changes. Third bodies were found
with orbital periods from 46 up to 84 years, and eccentricities from 0.0 to
0.78 for the selected binaries. The mass functions and the minimal masses of
such bodies were also calculated.Comment: 14 pages, 8 figure
Radial Velocity Studies of Close Binary Stars.III
Radial velocity measurements and simple sine-curve fits to the orbital
velocity variations are presented for the third set of ten contact binary
systems: CN And, HV Aqr, AO Cam, YY CrB, FU Dra, RZ Dra, UX Eri, RT LMi, V753
Mon, OU Ser. All systems but two are contact, double-line spectroscopic
binaries with four of them (YY CrB, FU Dra, V753 Mon, OU Ser) being the recent
discoveries of the Hipparcos satellite project. The most interesting object is
V753 Mon with the mass-ratio closest to unity among all contact systems (q =
0.970 pm 0.003) and large total mass ((M1+M2)sin^3i = 2.93 pm 0.06). Several of
the studied systems are prime candidates for combined light and radial-velocity
synthesis solutions.Comment: submitted for publication in Astronomical Journal; 3 figures, 2
table
Dwarf nova-type cataclysmic variable stars are significant radio emitters
We present 8–12 GHz radio light curves of five dwarf nova (DN) type cataclysmic variable stars (CVs) in outburst (RX And, U Gem, and Z Cam), or superoutburst (SU UMa and YZ Cnc), increasing the number of radio-detected DN by a factor of 2. The observed radio emission was variable on time-scales of minutes to days, and we argue that it is likely to be synchrotron emission. This sample shows no correlation between the radio luminosity and optical luminosity, orbital period, CV class, or outburst type; however, higher cadence observations are necessary to test this, as the measured luminosity is dependent on the timing of the observations in these variable objects. The observations show that the previously detected radio emission from SS Cyg is not unique in type, luminosity (in the plateau phase of the outburst), or variability time-scales. Our results prove that DN, as a class, are radio emitters in outburst
The Eruption of the Candidate Young Star ASASSN-15qi
Outbursts on young stars are usually interpreted as accretion bursts caused by instabilities in the disk or the star-disk connection. However, some protostellar outbursts may not fit into this framework. In this paper, we analyze optical and near-infrared spectra and photometry to characterize the 2015 outburst of the probable young star ASASSN-15qi. The mag brightening in the band was sudden, with an unresolved rise time of less than one day. The outburst decayed exponentially by 1 mag for 6 days and then gradually back to the pre-outburst level after 200 days. The outburst is dominated by emission from K gas. An explosive release of energy accelerated matter from the star in all directions, seen in a spectacular cool, spherical wind with a maximum velocity of 1000 km/s. The wind and hot gas both disappeared as the outburst faded and the source the source returned to its quiescent F-star spectrum. Nebulosity near the star brightened with a delay of 10-20 days. Fluorescent excitation of H is detected in emission from vibrational levels as high as , also with a possible time delay in flux increase. The mid-infrared spectral energy distribution does not indicate the presence of warm dust emission, although the optical photospheric absorption and CO overtone emission could be related to a gaseous disk. Archival photometry reveals a prior outburst in 1976. Although we speculate about possible causes for this outburst, none of the explanations are compelling