38 research outputs found
Five-Year Optical and Near Infrared Observations of the Extremely Slow Nova V1280 Scorpii
We present optical (, , , and ) and near
infrared (, and ) photometric and spectroscopic observations
of a classical nova V1280 Scorpii for five years from 2007 to 2011. Our
photometric observations show a declining event in optical bands shortly after
the maximum light which continues 250 days. The event is most probably
caused by a dust formation. The event is accompanied by a short ( 30
days) re-brightening episode ( 2.5 mag in ), which suggests a
re-ignition of the surface nuclear burning. After 2008, the band
observations show a very long plateau at around = 10.5 for more than 1000
days until April 2011 ( 1500 days after the maximum light). The nova had
taken a very long time ( 50 months) before entering the nebular phase
(clear detection of both [\ion{O}{iii}] 4959 and 5007) and is still continuing
to generate the wind caused by H-burning. The finding suggests that V1280 Sco
is going through the historically slowest evolution. The interval from the
maximum light (2007 February 16) to the beginning of the nebular phase is
longer than any previously known slow novae: V723 Cas (18 months), RR Pic (10
months), or HR Del (8 months). It suggests that the mass of a white dwarf in
the V1280 Sco system might be 0.6 M_\mathrm{\sun} or smaller. The distance,
based on our measurements of the expansion velocity combined with the directly
measured size of the dust shell, is estimated to be 1.1 0.5 kpc.Comment: 17 pages, 14 figures, accepted for publication in A&
Modeling of the Super-Eddington Phase for Classical Novae: Five IUE Novae
We present a light curve model for the super-Eddington luminosity phase of
five classical novae observed with IUE. Optical and UV light curves are
calculated based on the optically thick wind theory with a reduced effective
opacity for a porous atmosphere. Fitting a model light curve with the UV 1455
\AA light curve, we determine the white dwarf mass and distance to be (1.3
M_sun, 4.4 kpc) for V693 CrA, (1.05 M_sun, 1.8 kpc) for V1974 Cyg, (0.95 M_sun,
4.1 kpc) for V1668 Cyg, (1.0 M_sun, 2.1 kpc) for V351 Pup, and (1.0 M_sun, 4.3
kpc) for OS And.Comment: 9 pages including 8 figures, to appear in the Astrophysical Journa
Early evolution of the extraordinary Nova Del 2013 (V339 Del)
We determine the temporal evolution of the luminosity L(WD), radius R(WD) and
effective temperature Teff of the white dwarf (WD) pseudophotosphere of V339
Del from its discovery to around day 40. Another main objective was studying
the ionization structure of the ejecta. These aims were achieved by modelling
the optical/near-IR spectral energy distribution (SED) using low-resolution
spectroscopy (3500 - 9200 A), UBVRcIc and JHKLM photometry. During the fireball
stage (Aug. 14.8 - 19.9, 2013), Teff was in the range of 6000 - 12000 K, R(WD)
was expanding non-uniformly in time from around 66 to around 300 (d/3 kpc)
R(Sun), and L(WD) was super-Eddington, but not constant. After the fireball
stage, a large emission measure of 1.0-2.0E+62 (d/3 kpc)**2 cm**(-3)
constrained the lower limit of L(WD) to be well above the super-Eddington
value. The evolution of the H-alpha line and mainly the transient emergence of
the Raman-scattered O VI 1032 A line suggested a biconical ionization structure
of the ejecta with a disk-like H I region persisting around the WD until its
total ionization, around day 40. It is evident that the nova was not evolving
according to the current theoretical prediction. The unusual non-spherically
symmetric ejecta of nova V339 Del and its extreme physical conditions and
evolution during and after the fireball stage represent interesting new
challenges for the theoretical modelling of the nova phenomenon.Comment: 14 pages, 9 figures, 3 tables, accepted for Astronomy and
Astrophysic
The Stellar Composition of the Star Formation Region CMa R1 -- III. A new outburst of the Be star component in Z CMa
We report on a recent event in which, after more than a decade of slowly
fading, the visual brightness of the massive young binary Z CMa suddenly
started to rise by about 1 magnitude in December 1999, followed by a rapid
decline to its previous brightness over the next six months. This behaviour is
similar to that exhibited by this system around its eruption in February 1987.
A comparison of the intrinsic luminosities of the system with recent
evolutionary calculations shows that Z CMa may consist of a 16 M_sun B0 IIIe
primary star and a ~ 3 M_sun FUOr secondary with a common age of ~ 3 x 10^5 yr.
We also compare new high-resolution spectra obtained in Jan. and Feb. 2000,
during the recent rise in brightness, with archive data from 1991 and 1996. The
spectra are rich in emission lines, which originate from the envelope of the
early B-type primary star. The strength of these emission lines increased
strongly with the brightness of Z CMa. We interpret the collected spectral data
in terms of an accretion disc with atmosphere around the Herbig B0e component
of Z CMa, which has expanded during the outbursts of 1987 and 2000. A high
resolution profile of the 6300 A [O I] emission line, obtained by us in March
2002 shows an increase in flux and a prominent blue shoulder to the feature
extending to ~ -700 km/s, which was much fainter in the pre-outburst spectra.
We propose that this change in profile is a result of a strong change in the
collimation of a jet, as a result of the outburst at the start of this century.Comment: 22 pages, 12 figures, accepted for publication in MNRA
Excess mid-IR emission in Cataclysmic Variables
We present a search for excess mid-IR emission due to circumbinary material
in the orbital plane of cataclysmic variables (CVs). Our motivation stems from
the fact that the strong braking exerted by a circumbinary (CB) disc on the
binary system could explain several puzzles in our current understanding of CV
evolution. Since theoretical estimates predict that the emission from a CB disc
can dominate the spectral energy distribution (SED) of the system at
wavelengths > 5 microns, we obtained simultaneous visible to mid-IR SEDs for
eight systems. We report detections of SS Cyg at 11.7 microns and AE Aqr at
17.6 microns, both in excess of the contribution from the secondary star. In AE
Aqr, the IR likely originates from synchrotron-emitting clouds propelled by the
white dwarf. In SS Cyg, we argue that the observed mid-IR variability is
difficult to reconcile with simple models of CB discs and we consider free-free
emission from a wind. In the other systems, our mid-IR upper limits place
strong constraints on the maximum temperature of a putative CB disc. The
results show that if any sizeable CB disc are present in these systems, they
must be self-shadowed or perhaps dust-free, with the peak thermal emission
shifted to far-IR wavelengths.Comment: 14 pages, 6 figures, accepted for publication in MNRA
Evaluation of self-absorption of manganese emission lines in Laser Induced Breakdown Spectroscopy measurements
Spectral and luminosity classification for the cool components in symbiotic stars
The near infrared spectra of 12 S-type symbiotic stars and 78
comparison stars have been observed with moderate dispersion in five runs
from 1992 to 1997, the resolving power being , with a signal to noise ratio .
The triple-headed absorption band of TiO (8432, 8422 and
8452 Ã…) emerges when a star is later than M2, and the depth of the TiO
absorption band is very sensitive to the spectral type (ST) and insensitive to
the luminosity class of the star. We fit a curve of spectral type against the
index of the absorption depth of this band with a standard deviation
of a subdivision of one spectral type.
The IR CaII triplet (8498, 8542, 8662 Ã…),
Fe I 8689 Å, and  Fe I 8675 Å are good luminosity indicators although
the equivalent widths (EWs) of these lines clearly decrease
for a star later than M3. When the star is a supergiant, the lines have a
smaller central residual intensity and broader wings
than in the case of a normal giant.
The Ca II 8662 Å/Fe I 8675 Å and Fe I 8689 Å/Fe I 8675 Å ratios are also
good luminosity indicators for K-type giants. The latter is particularly useful
when there are abundance anomalies. The metal-poor symbiotic star AG Dra is
classified as a Ib or II giant, as is TX CVn, on the basis of
Fe I 8689 Ã…/Fe I 8675 Ã…. Â 9 other symbiotic stars containing M-type cool
components are classified as giants by direct comparison and quantitative
analysis. Due to there being no known good ratio indicator of luminosity for
M-type stars in the band studied and because there is no metal abundance data
for the symbiotic stars studied by us except for AG Dra, the results for
these 9 symbiotic stars are only preliminary.
The infrared Ca II triplet of most symbiotic stars clearly varies between
the different observing runs. The different luminosity classes given to
the same symbiotic star are probably caused by the variability of
the lines of ionized elements, while in some cases they are affected by a low
metal abundance