24 research outputs found
The Absolute Parameters of The Detached Eclipsing Binary V482 Per
We present the results of the spectroscopic, photometric and orbital period
variation analyses of the detached eclipsing binary \astrobj{V482~Per}. We
derived the absolute parameters of the system (M = 1.51 M,
M = 1.29 M, R = 2.39 R, R = 1.45
R, L = 10.15 L, L = 3.01 L) for the
first time in literature, based on an analysis of our own photometric and
spectroscopic observations. We confirm the nature of the variations observed in
the system's orbital period, suggested to be periodic by earlier works. A light
time effect due to a physically bound, star-sized companion (M = 2.14
M) on a highly eccentric (e = 0.83) orbit, seems to be the most
likely cause. We argue that the companion can not be a single star but another
binary instead. We calculated the evolutionary states of the system's
components, and we found that the primary is slightly evolving after the Main
Sequence, while the less massive secondary lies well inside it.Comment: Published in New Astronomy, Vol. 41, p. 42-4
Hubble Space Telescope Photometry of Globular Clusters in M81
We perform aperture photometry and profile fitting on 419 globular cluster
(GC) candidates with mV \leq 23 mag identified in Hubble Space Telescope
Advanced Camera for Surveys BVI imaging, and estimate the effective radii of
the clusters. We identify 85 previously known spectroscopically-confirmed
clusters, and newly identify 136 objects as good cluster candidates within the
3{\sigma} color and size ranges defined by the spectroscopically confirmed
clusters, yielding a total of 221 probable GCs. The luminosity function peak
for the 221 probable GCs with estimated total dereddening applied is V ~(20.26
\pm 0.13) mag, corresponding to a distance of ~3.7\pm0.3 Mpc. The blue and red
GC candidates, and the metal-rich (MR) and metal-poor (MP) spectroscopically
confirmed clusters, are similar in half-light radius, respectively. Red
confirmed clusters are about 6% larger in median half-light radius than blue
confirmed clusters, and red and blue good GC candidates are nearly identical in
half-light radius. The total population of confirmed and "good" candidates
shows an increase in half-light radius as a function of galactocentric
distance.Comment: 42 figures, 14 pages, accepted to A
Asteroseismology of massive stars with the TESS mission: the runaway Beta Cep pulsator PHL 346 = HN Aqr
We report an analysis of the first known Beta Cep pulsator observed by the
TESS mission, the runaway star PHL 346 = HN Aqr. The star, previously known as
a singly-periodic pulsator, has at least 34 oscillation modes excited, 12 of
those in the g-mode domain and 22 p modes. Analysis of archival data implies
that the amplitude and frequency of the dominant mode and the stellar radial
velocity were variable over time. A binary nature would be inconsistent with
the inferred ejection velocity from the Galactic disc of 420 km/s, which is too
large to be survivable by a runaway binary system. A kinematic analysis of the
star results in an age constraint (23 +- 1 Myr) that can be imposed on
asteroseismic modelling and that can be used to remove degeneracies in the
modelling process. Our attempts to match the excitation of the observed
frequency spectrum resulted in pulsation models that were too young. Hence,
asteroseismic studies of runaway pulsators can become vital not only in tracing
the evolutionary history of such objects, but to understand the interior
structure of massive stars in general. TESS is now opening up these stars for
detailed asteroseismic investigation.Comment: accepted for ApJ
Radial Velocity Studies of Close Binary Stars. IX
Radial-velocity measurements and sine-curve fits to the orbital velocity
variations are presented for the eighth set of ten close binary systems: AB
And, V402 Aur, V445 Cep, V2082 Cyg, BX Dra, V918 Her, V502 Oph, V1363 Ori, KP
Peg, V335 Peg. Half of the systems (V445 Cep, V2082 Cyg, V918 Her, V1363 Ori,
V335 Peg) were discovered photometrically by the Hipparcos mission and all
systems are double-lined (SB2) contact binaries. The broadening function method
permitted improvement of the orbital elements for AB And and V502 Oph. The
other systems have been observed for radial velocity variations for the first
time; in this group are five bright (V<7.5) binaries: V445 Cep, V2082 Cyg, V918
Her, KP Peg and V335 Peg. Several of the studied systems are prime candidates
for combined light and radial-velocity synthesis solutions.Comment: 17+ pages, 2 tables, 4 figure
Spitzer Observations of the Predicted Eddington Flare from Blazar OJ 287
Binary black hole (BH) central engine description for the unique blazar OJ
287 predicted that the next secondary BH impact-induced bremsstrahlung flare
should peak on 2019 July 31. This prediction was based on detailed general
relativistic modeling of the secondary BH trajectory around the primary BH and
its accretion disk. The expected flare was termed the Eddington flare to
commemorate the centennial celebrations of now-famous solar eclipse
observations to test general relativity by Sir Arthur Eddington. We analyze the
multi-epoch Spitzer observations of the expected flare between 2019 July 31 and
2019 September 6, as well as baseline observations during 2019 February-March.
Observed Spitzer flux density variations during the predicted outburst time
display a strong similarity with the observed optical pericenter flare from OJ
287 during 2007 September. The predicted flare appears comparable to the 2007
flare after subtracting the expected higher base-level Spitzer flux densities
at 3.55 and 4.49 m compared to the optical R-band. Comparing the 2019 and
2007 outburst lightcurves and the previously calculated predictions, we find
that the Eddington flare arrived within 4 hours of the predicted time. Our
Spitzer observations are well consistent with the presence of a nano-Hertz
gravitational wave emitting spinning massive binary BH that inspirals along a
general relativistic eccentric orbit in OJ 287. These multi-epoch Spitzer
observations provide a parametric constraint on the celebrated BH no-hair
theorem.Comment: 8 pages, 4 figures, 1 table, to appear in ApJ
Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae
We systematically surveyed period variations of superhumps in SU UMa-type
dwarf novae based on newly obtained data and past publications. In many
systems, the evolution of superhump period are found to be composed of three
distinct stages: early evolutionary stage with a longer superhump period,
middle stage with systematically varying periods, final stage with a shorter,
stable superhump period. During the middle stage, many systems with superhump
periods less than 0.08 d show positive period derivatives. Contrary to the
earlier claim, we found no clear evidence for variation of period derivatives
between superoutburst of the same object. We present an interpretation that the
lengthening of the superhump period is a result of outward propagation of the
eccentricity wave and is limited by the radius near the tidal truncation. We
interpret that late stage superhumps are rejuvenized excitation of 3:1
resonance when the superhumps in the outer disk is effectively quenched. Many
of WZ Sge-type dwarf novae showed long-enduring superhumps during the
post-superoutburst stage having periods longer than those during the main
superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to
be strongly correlated with the fractional superhump excess, or consequently,
mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with
multiple rebrightenings tend to have smaller period derivatives and are
excellent candidate for the systems around or after the period minimum of
evolution of cataclysmic variables (abridged).Comment: 239 pages, 225 figures, PASJ accepte
Polarization and Spectral Energy Distribution in OJ 287 during the 2016/17 Outbursts
We report optical photometric and polarimetric observations of the
blazar OJ 287 gathered during 2016/17. The high level of activity,
noticed after the General Relativity Centenary flare, is argued to be
part of the follow-up flares that exhibited high levels of polarization
and originated in the primary black hole jet. We propose that the
follow-up flares were induced as a result of accretion disk
perturbations, traveling from the site of impact towards the primary
SMBH. The timings inferred from our observations allowed us to estimate
the propagation speed of these perturbations. Additionally, we make
predictions for the future brightness of OJ 287.</p
Long-Term Optical Monitoring of Blazars
Systematic monitoring of specific targets in the optical regime was historically applied on a very narrow sample of known variable stars. The discovery of blazars in the 20th century brought to the foreground the need for new global sky surveys, covering the entire sky and fainter sources. Full-sky surveys are conducted more easily from space observatories, while radio telescopes perform follow up observations from the ground. Blazars are detected in a wide range of energies, while they exhibit strong variability in various wavelengths from γ-rays and X-rays to the optical and radio domain. This results in a detailed classification, according to their emission properties in each region. The rapid variability in optical domain makes blazars interesting targets for optical sky surveys, offering a new opportunity to study their variability in the time domain. Digital sky surveys in optical and near-IR found a fertile ground with the aid of sensitive sensors. Only a few dedicated programs are focusing on blazar variability, a trend which evolved rapidly in the last decade. Modern techniques, in combination with dedicated sky survey programs lead towards a new era of long-term monitoring of blazars, aiming towards the search or variability on various time scales. In this work, an overview of blazar optical surveys and monitoring projects is given, addressing the major points of each one, and highlighting the constraints that the long-term study of blazars will bring through future international campaigns