37 research outputs found
Study of the fastest classical nova, V1674 Her: Photoionization and Morpho-kinemetic model analysis
We present the results of the investigation of the nova V1674 Her (2021),
recognised as the swiftest classical nova, with days. The
distance to the nova is estimated to be 4.97 kpc. The mass and radius of the WD
are calculated to be and ,
respectively. Over the course of one month following the outburst, V1674 Her
traversed distinct phases -- pre-maxima, early decline, nebular, and coronal --
displaying a remarkably swift transformation. The nebular lines emerged on day
10.00, making it the classical nova with the earliest observed commencement to
date. We modelled the observed optical spectrum using the photoionization code
\textsc{cloudy}. From the best-fitting model we deduced different physical and
chemical parameters associated withe the system. The temperature and luminosity
of the central ionizing sources are found in the range of K and \ergs, respectively. Elements such as
He, O, N, and Ne are found to be overabundant compared to solar abundance in
both the nebular and coronal phases. According to the model, Fe II abundance
diminishes while Ne abundance increases, potentially elucidating the rare
hybrid transition between Fe and He/N nova classes. The ejected mass across all
epochs spanned from . Morpho-kinematic
modelling utilising \textsc{shape} revealed that the nova V1674 Her possesses a
bipolar structure with an equatorial ring at the centre and an inclination
angle of i = 67 1.5.Comment: 19 pages, 17 figures, 6 table
Long-term monitoring of the short period SU UMa-type dwarf nova, V844 Herculis
We report on time-resolved CCD photometry of four outbursts of a short-period
SU UMa-type dwarf nova, V844 Herculis. We successfully determined the mean
superhump periods to be 0.05584(64) days, and 0.055883(3) for the 2002 May
superoutburst, and the 2006 April-May superoutburst, respectively. During the
2002 October observations, we confirmed that the outburst is a normal outburst,
which is the first recorded normal outburst in V844 Her. We also examined
superhump period changes during 2002 May and 2006 April-May superoutbursts,
both of which showed increasing superhump period over the course of the plateau
stage. In order to examine the long-term behavior of V844 Her, we analyzed
archival data over the past ten years since the discovery of this binary.
Although photometry is not satisfactory in some superoutbursts, we found that
V844 Her showed no precursors and rebrightenings. Based on the long-term light
curve, we further confirmed V844 Her has shown almost no normal outbursts
despite the fact that the supercycle of the system is estimated to be about 300
days. In order to explain the long-term light curves of V844 Her, evaporation
in the accretion disk may play a role in the avoidance of several normal
outbursts, which does not contradict with the relatively large X-ray luminosity
of V844 Her.Comment: 10 pages, 11 figures, accepted for PAS