29 research outputs found
Towards a better classification of unclear eruptive variables: the cases of V2492 Cyg, V350 Cep, and ASASSN-15qi
Eruptive variables are young stars that show episodic variations of
brightness: EXors/FUors variations are commonly associated with enhanced
accretion outbursts occurring at intermittent cadence of months/years (EXors)
and decades/centuries (FUors). Variations that can be ascribed to a variable
extinction along their line of sight are instead classified as UXors. We aim at
investigating the long-term photometric behaviour of three sources classified
as eruptive variables. We present data from the archival plates of the Asiago
Observatory relative to the fields where the targets are located. For the sake
of completeness we have also analysed the Harvard plates of the same regions
that cover a much longer historical period, albeit at a lower sensitivity,
however we are only able to provide upper limits. A total of 273 Asiago plates
were investigated, providing a total of more than 200 magnitudes for the three
stars, which cover a period of about 34 yr between 1958 and 1991. We have
compared our data with more recently collected literature data. Our plates
analysis of V2492 Cyg provides historical upper limits that seem not to be
compatible with the level of the activity monitored during the last decade.
Therefore, recently observed accretion phenomena could be associated with the
outbursting episodes, more than repetitive obscuration. While a pure extinction
does not seem the only mechanism responsible for the ASASSN-15qi fluctuations,
it can account quite reasonably for the recent V350 Cep variations.Comment: 12 pages, accepted by A&
Solar differential rotation in the period 1964 - 2016 determined by the Kanzelh\"ohe data set
The main aim of this work is to determine the solar differential rotation by
tracing sunspot groups during the period 1964-2016, using the Kanzelh\"ohe
Observatory for Solar and Environmental Research (KSO) sunspot drawings and
white light images. Two procedures for the determination of the heliographic
positions were applied: an interactive procedure on the KSO sunspot drawings
(1964 - 2008, solar cycles nos. 20 - 23) and an automatic procedure on the KSO
white light images (2009 - 2016, solar cycle no. 24). For the determination of
the synodic angular rotation velocities two different methods have been used: a
daily shift (DS) method and a robust linear least-squares fit (rLSQ) method.
Afterwards, the rotation velocities had to be converted from synodic to
sidereal, which were then used in the least-squares fitting for the solar
differential rotation law. For the test data from 2014, we found the rLSQ
method for calculating rotational velocities to be more reliable than the DS
method. The best fit solar differential rotation profile for the whole time
period is = (14.47 0.01) - (2.66 0.10)
(deg/day) for the DS method and = (14.50 0.01) - (2.87
0.12) (deg/day) for the rLSQ method. A barely noticeable north -
south asymmetry is observed for the whole time period 1964 - 2016 in the
present paper. Rotation profiles, using different data sets (e.g. Debrecen
Photoheliographic Data, Greenwich Photoheliographic Results), presented by
other authors for the same time periods and the same tracer types, are in good
agreement with our results. Therefore, the KSO data set is suitable for the
investigation of the long-term variabilities in the solar rotation profile
Symbiotic stars on Asiago archive plates. I
The rich plate archive of the Asiago observatory has been searched for plates
containing the symbiotic stars AS 323, Ap 3-1, CM Aql, V1413 Aql (=AS 338),
V443 Her, V627 Cas (=AS 501) and V919 Sgr. The program objects have been found
on 602 plates, where their brightness has been estimated against the UBVRI
photometric sequences calibrated by Henden and Munari (2000, A&AS 143, 343). AS
323 is probably eclipsing, with a preliminary P=197.6 day period. If confirmed,
it would be the shortest orbital period known among symbiotic stars. CM Aql
does not seem to undergo a series of outbursts, its lightcurve being instead
modulated by a large amplitude sinusoidal variation with a P~1058 day period.
V627 Cas presents a secular trend in agreement with the possible post-AGB
nature of its cool component.Comment: A&A in pres
Historical light curve and search for previous outbursts of Nova KT Eridani (2009)
Context. Nova Eridani (2009) caught the eye of the nova community due to its
fast decline from maximum, which was initially missed, and its subsequent
development in the radio and X-ray wavelengths. This system also exhibits
properties similar to those of the much smaller class of recurrent novae;
themselves potential progenitors of Type Ia Supernovae. Aims. We aim to
determine the nature and physical parameters of the KT Eri progenitor system.
Methods. We searched the Harvard College Observatory archive plates for the
progenitor of KT Eri to determine the nature of the system, particularly the
evolutionary stage of the secondary.We used the data obtained to search for any
periodic signal and the derived luminosity to estimate a recurrence timescale.
Furthermore, by comparing the colours of the quiescent system on a
colour-magnitude diagram we may infer the nature of the secondary star.
Results. We identified the progenitor system of KT Eri and measured a quiescent
magnitude of = 14.7 \pm 0.4. No previous outburst was found. However, we
suggest that if the nova is recurrent it should be on a timescale of centuries.
We find a periodicity at quiescence of 737 days which may arise from reflection
effects and/or eclipses in the central binary. The periodicity and the
quiescence magnitude of the system suggest that the secondary star is evolved
and likely in, or ascending, the Red Giant Branch. A second period is evident
at 376 days which has a sinusoidal like light curve. Furthermore, the outburst
amplitude of ~ 9 magnitudes is inconsistent with those expected for fast
classical novae (~ 17 magnitudes) which may lend further support for an evolved
secondary. (Abridged)Comment: 6 pages, 5 figures, accepted for publication in A&
Optical photometric and spectral study of the new FU Orionis object V2493 Cygni (HBC 722)
Aims. We present new results from optical photometric and spectroscopic observations of the eruptive pre-main sequence star V2493 Cyg (HBC 722). The object has continued to undergo significant brightness variations over the past few months and is an ideal target for follow-up observations.
Methods. We carried out CCD BVRI photometric observations in the field of V2493 Cyg (“Gulf of Mexico”) from August 1994 to April 2012, i.e. at the pre-outburst states and during the phases of the outburst. We acquired high, medium, and low resolution spectroscopy of V2493 Cyg during the outburst. To study the pre-outburst variability of the target and construct its historical light curve, we searched for archival observations in photographic plate collections. Both CCD and photographic observations were analyzed using 15 comparison stars in the field of V2493 Cyg.
Results. The pre-outburst photographic and CCD photometric observations of V2493 Cyg show low-amplitude light variations typical of T Tauri stars. The recent photometric data show a slow light decrease from October 2010 to June 2011 followed by an increase in brightness that continued until early 2012. The spectral observations of V2493 Cyg are typical of FU Orionis stars absorption spectra with strong P Cyg profiles of Hα and Na I D lines. On the basis of photometric monitoring performed over the past two years, the spectral properties at the maximal light, as well as the shape of long-term light curves, we confirm that the observed outburst of V2493 Cyg is of FU Orionis type
Symbiotic stars on Asiago archive plates. II
The Asiago photographic archive has been searched for plates containing the
symbiotic stars Hen 2-468, QW Sge, LT Del, V407 Cyg, K 3-9, V335 Vul, FG Ser
and Draco C-1. A total of 635 plates imaging the program stars have been found
and the brightness estimated using the Henden & Munari (2000) UBVRI photometric
sequences. These historical data have allowed for the first time the
determination of the orbital periods of Hen 2-468 (774 days) and QW Sge (390.5
days), a significant improvement in the orbital period of LT Del (465.6 days)
and for V407 Cyg an evaluation of the Mira's pulsation period and complex
lightcurve shape in the red (R and I bands). Some previously unknown outbursts
have been discovered too. (Paper I: Munari et al. 2001, A&A 370, 503)Comment: A&A, in pres
A Comparison of Solar Cycle Variations in the Equatorial Rotation Rates of the Sun's Subsurface, Surface, Corona, and Sunspot Groups
Using the Solar Optical Observing Network (SOON) sunspot-group data for the
period 1985-2010, the variations in the annual mean equatorial-rotation rates
of the sunspot groups are determined and compared with the known variations in
the solar equatorial-rotation rates determined from the following data: i) the
plasma rotation rates at 0.94Rsun, 0.95Rsun,...,1.0Rsun measured by Global
Oscillation Network Group (GONG) during the period 1995-2010, ii) the data on
the soft X-ray corona determined from Yohkoh/SXT full disk images for the years
1992-2001, iii) the data on small bright coronal structures (SBCS) which were
traced in Solar and Heliospheric Observatory (SOHO)/EIT images during the
period 1998-2006, and iv) the Mount Wilson Doppler-velocity measurements during
the period 1986-2007. A large portion (up to approximate 30 deg latitude) of
the mean differential-rotation profile of the sunspot groups lies between those
of the internal differential-rotation rates at 0.94Rsun and 0.98Rsun.The
variation in the yearly mean equatorial-rotation rate of the sunspot groups
seems to be lagging that of the equatorial-rotation rate determined from the
GONG measurements by one to two years.The amplitude of the latter is very
small.The solar-cycle variation in the equatorial-rotation rate of the solar
corona closely matches that determined from the sunspot-group data.The
variation in the equatorial-rotation rate determined from the Mount Wilson
Doppler-velocity data closely resembles the corresponding variation in the
equatorial-rotation rate determined from the sunspot-group data that included
the values of the abnormal angular motions (> 3 deg per day) of the sunspot
groups. Implications of these results are pointed out.Comment: 22 pages, 10 figures, accepted by Solar Physic
Morpho-kinematical modelling of Nova Eridani 2009 (KT Eri)
Modelling the morphology of a nova outburst provides valuable information on the shaping mechanism in operation at early stages following the outburst. We performed morphokinematical studies, using shape, of the evolution of the Hα line profile following the outburst of the nova KT Eridani. We applied a series of geometries in order to determine the morphology of the system. The best fit morphology was that of a dumbbell structure with a ratio
between the major to minor axis of 4:1, with an inclination angle of 58+6−7 degrees and a maximum expansion velocity of 2800±200 km s−1. Although, we found that it is possible to define the overall structure of the system, the radial density profile of the ejecta is much more difficult
to disentangle. Furthermore, morphology implied here may also be consistent with the presence of an evolved secondary as suggested by various authors
Reconstructing Historical Light Curves of Symbiotic Stars and Novae
We reconstructed photometric histories of symbiotic stars and novae from direct inspection and measurement of photographic plates preserved at historical archives. We have completed the digging of the rich Asiago archive, and have started working on the Harvard plate stack, while other plate collections should be added soon. For homogeneity, we use the same UBV RCIC photometric comparison sequences used in current CCD observations. This data harvest has permitted the discovery of past undetected outbursts and secular trends, or to derive previously unknown orbital periods and recurrence times, which are essential to constrain the nature of these capricious and variegated active binaries
CH Cygni 1987-89: The inactive state as a precursor to the new outburst
In order to help answering the question generally posed for symbiotic stars: are the
apparently inactive periods quiescent at all, or should they be regarded merely
as a transition between adjacent outbursts, we tried to establish correlation between the
subtle phenomena in the time evolution of the cool giant's photosphere and emission line
profiles of the symbiotic star CH Cygni during the period 1987-89. Optical spectra of
this star in its inactive state taken at the Haute Provence Observatory as well as the spectra
of late type giant's of the same spectral type have been used. The comparison of the
results obtained suggests that the time evolution of the physical parameters of CH Cyg
reflect the symbiotic phenomena rather than the intrinsic variability of the cool
component. The time behaviour of the Balmer emission line profiles rules out the general
validity of the established models. An acceptable model valid at least for the observed
period has been proposed. According to it, an envelope of variable optical thickness
surrounds the hot component. The development
of its inner radius, of and
line profiles and of the
nebular line leads to the conclusion that the inactive state is not stationary, but is gradually evolving in time toward the new activity of the
star