25 research outputs found
Spectra of V1405 Cas at the very beginning indicate a low-mass ONeMg white dwarf progenitor
The lowest possible mass of ONeMg white dwarfs (WDs) has not been clarified
despite its importance in the formation and evolution of WDs. We tackle this
issue by studying the properties of V1405 Cas (Nova Cassiopeiae 2021), which is
an outlier given a combination of its very slow light-curve evolution and the
recently reported neon-nova identification. We report its rapid spectral
evolution in the initial phase, covering 9.88, 23.77, 33.94, 53.53, 71.79, and
81.90 hours after the discovery. The first spectrum is characterized by lines
from highly-ionized species, most noticeably He II and N III. These lines are
quickly replaced by lower-ionization lines, e.g., N II, Si II, and O I. In
addition, Al II (6237 \r{A}) starts emerging as an emission line at the second
epoch. We perform emission-line strength diagnostics, showing that the density
and temperature quickly decrease toward later epochs. This behavior, together
with the decreasing velocity seen in H, H, and He I, indicates
that the initial nova dynamics is reasonably well described by an expanding
fireball on top of an expanding photosphere. Interestingly, the strengths of
the N III and Al II indicate large abundance enhancement, pointing to an ONeMg
WD progenitor as is consistent with its neon-nova classification. Given its
low-mass nature inferred by the slow light-curve evolution and relatively
narrow emission lines, it provides a challenge to the stellar evolution theory
that predicts the lower limit of the ONeMg WD mass being 1.1 .Comment: 15 pages, 5 figures, 2 tables, accepted to Ap
Multicolor and multi-spot observations of Starlink's Visorsat
This study provides the results of simultaneous multicolor observations for
the first Visorsat (STARLINK-1436) and the ordinary Starlink satellite,
STARLINK-1113 in the , , , , , , , ,
, , , and bands to quantitatively investigate the extent to
which Visorsat reduces its reflected light. Our results are as follows: (1) in
most cases, Virorsat is fainter than STARLINK-1113, and the sunshade on
Visorsat, therefore, contributes to the reduction of the reflected sunlight;
(2) the magnitude at 550 km altitude (normalized magnitude) of both satellites
often reaches the naked-eye limiting magnitude ( 6.0); (3) from a blackbody
radiation model of the reflected flux, the peak of the reflected components of
both satellites is around the band; and (4) the albedo of the near infrared
range is larger than that of the optical range. Under the assumption that
Visorsat and STARLINK-1113 have the same reflectivity, we estimate the covering
factor, , of the sunshade on Visorsat, using the blackbody radiation
model: the covering factor ranges from . From
the multivariable analysis of the solar phase angle (Sun-target-observer), the
normalized magnitude, and the covering factor, the phase angle versus covering
factor distribution presents a moderate anti-correlation between them,
suggesting that the magnitudes of Visorsat depend not only on the phase angle
but also on the orientation of the sunshade along our line of sight. However,
the impact on astronomical observations from Visorsat-designed satellites
remains serious. Thus, new countermeasures are necessary for the Starlink
satellites to further reduce reflected sunlight.Comment: 31 pages, 9 figures, published in PAS
First Detection of Two Superoutbursts during Rebrightening Phase of a WZ Sge-type Dwarf Nova: TCP J21040470+4631129
We report photometric and spectroscopic observations and analysis of the 2019
superoutburst of TCP J21040470+4631129. This object showed a 9-mag
superoutburst with early superhumps and ordinary superhumps, which are the
features of WZ Sge-type dwarf novae. Five rebrightenings were observed after
the main superoutburst. The spectra during the post-superoutburst stage showed
the Balmer, He I and possible sodium doublet features. The mass ratio is
derived as 0.0880(9) from the period of the superhump. During the third and
fifth rebrightenings, growing superhumps and superoutbursts were observed,
which have never been detected during a rebrightening phase among WZ Sge-type
dwarf novae with multiple rebrightenings. To induce a superoutburst during the
brightening phase, the accretion disk was needed to expand beyond the 3:1
resonance radius of the system again after the main superoutburst. These
peculiar phenomena can be explained by the enhanced viscosity and large radius
of the disk suggested by the higher luminosity and the presence of late-stage
superhumps during the post-superoutburst stage, plus by more mass supply from
the cool mass reservoir and/or from the secondary because of the enhanced mass
transfer than those of other WZ Sge-type dwarf novae.Comment: 13 pages, 10 figures, accepted for publication in PAS
First detection of two superoutbursts during rebrightening phase of a WZ Sge-type Dwarf Nova : TCP J21040470+4631129
We report on photometric and spectroscopic observations and analysis of the 2019 superoutburst of TCP J21040470+4631129. This object showed a 9 mag superoutburst with early superhumps and ordinary superhumps, which are the features of WZ Sge-type dwarf novae. Five rebrightenings were observed after the main superoutburst. The spectra during the post-superoutburst stage showed Balmer, He I, and possible sodium doublet features. The mass ratio is derived as 0.0880(9) from the period of the superhump. During the third and fifth rebrightenings, growing superhumps and superoutbursts were observed, which have never been detected during a rebrightening phase among WZ Sge-type dwarf novae with multiple rebrightenings. To induce a superoutburst during the brightening phase, the accretion disk needs to have expanded beyond the 3 : 1 resonance radius of the system again after the main superoutburst. These peculiar phenomena can be explained by the enhanced viscosity and large radius of the accretion disk suggested by the higher luminosity and the presence of late-stage superhumps during the post-superoutburst stage, plus by more mass supply from the cool mass reservoir and/or from the secondary because of the enhanced mass transfer than those of other WZ Sge-type dwarf novae.peer-reviewe
Spectroscopic and photometric observations of dwarf nova superoutbursts by the 3.8 m telescope Seimei and the Variable Star Network
arXiv:2104.04948v1et al.We present spectroscopic and photometric observations of 17 dwarf-nova superoutbursts obtained by KOOLS-IFU mounted on the 3.8 m telescope Seimei at the Okayama Observatory of Kyoto University and through the Variable Star Network collaboration (VSNET). Our spectroscopic observations for six outbursts were performed within 1 d of their optical peak. 11 objects (TCP J00590972+3438357, ASASSN-19ado, TCP J06073081−0101501, ZTF20aavnpug, ASASSN-19ady, MASTER OT J061642.05+435617.9, TCP J20034647+1335125, ASASSN-20kv, ASASSN-20kw, MASTER OT J213908.79+161240.2, and ASASSN-20mf) were previously unknown systems, and our observations enabled quick classification of their transient type. These results illustrate that the Seimei telescope has the capability to conduct quick follow-up observations of unknown transients. Our photometric observations yielded that 11 of the objects are WZ Sge-type dwarf novae and their candidates, and the other six are SU UMa-type dwarf novae and their candidates. The He ii 4686 Å emission line was clearly detected among ASASSN-19ado, TCP J06073081−0101501 and MASTER OT J213908.79+161240.2, the association of which with a spiral arm structure in an accretion disk has been suggested in previous studies. Our result suggests that a higher-inclination system shows a stronger emission line of He ii 4686 Å, as well as larger-amplitude early superhumps.Maeda acknowledges support from the Japan Society for the Promotion of Science (JSPS) KAKENHI grant JP18H05223, JP20H00174, and JP20H04737. U. Burgaz acknowledges the support provided by the Turkish Scientific and Technical Research Council (TÜBITAK2211C and 2214A). This work was supported by the project
APVV-15-0458 “Interacting binaries - Key for the Understanding of the Universe”. This work was supported by the Slovak Research and Development Agency under the contract No. APVV15-0458 and by the Slovak Academy of Sciences grant VEGA
No. 2/0030/21. The authors from Sternberg institute thank the Program of Development of Lomonosov MSU ‘Leading Scientific Schools’. A.A.B, N.P.I. and M.A.B. (SAI MSU) are
supported by the Interdisciplinary Scientific and Educational School of Moscow University ’Fundamental and Applied Space Research’. This research was partly supported by the Slovak Academy of Sciences grant VEGA No. 2/0030/21.Peer reviewe
Applying artificial intelligence to disease staging: Deep learning for improved staging of diabetic retinopathy.
Disease staging involves the assessment of disease severity or progression and is used for treatment selection. In diabetic retinopathy, disease staging using a wide area is more desirable than that using a limited area. We investigated if deep learning artificial intelligence (AI) could be used to grade diabetic retinopathy and determine treatment and prognosis.The retrospective study analyzed 9,939 posterior pole photographs of 2,740 patients with diabetes. Nonmydriatic 45° field color fundus photographs were taken of four fields in each eye annually at Jichi Medical University between May 2011 and June 2015. A modified fully randomly initialized GoogLeNet deep learning neural network was trained on 95% of the photographs using manual modified Davis grading of three additional adjacent photographs. We graded 4,709 of the 9,939 posterior pole fundus photographs using real prognoses. In addition, 95% of the photographs were learned by the modified GoogLeNet. Main outcome measures were prevalence and bias-adjusted Fleiss' kappa (PABAK) of AI staging of the remaining 5% of the photographs.The PABAK to modified Davis grading was 0.64 (accuracy, 81%; correct answer in 402 of 496 photographs). The PABAK to real prognosis grading was 0.37 (accuracy, 96%).We propose a novel AI disease-staging system for grading diabetic retinopathy that involves a retinal area not typically visualized on fundoscopy and another AI that directly suggests treatments and determines prognoses
First detection of two superoutbursts during the rebrightening phase of a WZ Sge-type dwarf nova: TCP J21040470+4631129
arXiv:2004.10508v1et al.We report on photometric and spectroscopic observations and analysis of the 2019 superoutburst of TCP J21040470+4631129. This object showed a 9 mag superoutburst with early superhumps and ordinary superhumps, which are the features of WZ Sge-type dwarf novae. Five rebrightenings were observed after the main superoutburst. The spectra during the post-superoutburst stage showed Balmer, He I, and possible sodium doublet features. The mass ratio is derived as 0.0880(9) from the period of the superhump. During the third and fifth rebrightenings, growing superhumps and superoutbursts were observed, which have never been detected during a rebrightening phase among WZ Sge-type dwarf novae with multiple rebrightenings. To induce a superoutburst during the brightening phase, the accretion disk needs to have expanded beyond the 3 : 1 resonance radius of the system again after the main superoutburst. These peculiar phenomena can be explained by the enhanced viscosity and large radius of the accretion disk suggested by the higher luminosity and the presence of late-stage superhumps during the post-superoutburst stage, plus by more mass supply from the cool mass reservoir and/or from the secondary because of the enhanced mass transfer than those of other WZ Sge-type dwarf novae.N. Narita is supported by JSPS KAKENHI Grant Numbers JP18H01265 and JP18H05439, and JST PRESTO Grant Number JPMJPR1775. M. Tamura is supported by MEXT/JSPS KAKENHI Grant Nos. 18H05442, 15H02063, and 22000005. P. A. Dubovsky, T. Medulka, and I. Kudzej acknowledge support by NSF AST-1751874 and the Cottrell scholarship from the Research Corporation for Science Advancement and by the Slovak Research and Development Agency under the contract No. APVV-15-0458. A. Zubareva, A. Belinski, A. Dodin, M. Burlak, N. Ikonnikova, E. Mishin, and S. Potanin acknowledge the support from the Program of development of M.V. Lomonosov Moscow State University (Leading Scientific School “Physics of stars, relativistic objects and galaxies”). E. P. Pavlenko, O. I. Antonyuk, and Ju. V. Bbabina acknowledge support by the RSF grant 19-72-10063.Peer reviewe