scholarly journals TESS photometry of extreme helium stars PV Tel and V821 Cen

2020 ◽  
Vol 495 (1) ◽  
pp. L135-L138 ◽  
Author(s):  
C Simon Jeffery ◽  
Geert Barentsen ◽  
Gerald Handler
Keyword(s):  
Light Curve ◽  
Time Scales ◽  
Characteristic Time ◽  
Satellite Observations ◽  
Light Curves ◽  
Single Site ◽  
Helium Stars ◽  
First Time

ABSTRACT PV Tel variables are extreme helium (EHe) stars known to be intrinsic light and velocity variable on characteristic time-scales of 0.1–25 d. With two exceptions, they are best described as irregular. Light curves have invariably been obtained from single-site terrestrial observatories. We present Transiting Exoplanet Survey Satellite observations of two bright EHe stars, Popper’s star (V821 Cen) and Thackeray’s star (PV Tel). PV Tel is variable on time-scales previously reported. V821 Cen is proven to be variable for the first time. Neither light curve shows any evidence of underlying regularity. Implications are considered.

PNN NGC 246: A Complex Photometric Behaviour That Requires Wet

2003 ◽  
Vol 12 (1) ◽  
Author(s):  
J. M. González Pérez ◽  
J.-E. Solheim ◽  
T. N. Dorokhova ◽  
N. I. Dorokhov
Keyword(s):  
Wavelet Analysis ◽  
Light Curve ◽  
Time Scales ◽  
Light Curves ◽  
Single Site ◽  
Harmonic Structure ◽  
Peculiar Characteristic

AbstractWe present a study over three single-site campaigns to investigate the photometric behaviour of the PNN NGC 246. We observed this object in 2000 and 2001. The analysis of the light curves indicates complex and variable temporal spectra. Using wavelet analysis we have found evidences for changes on time scales of hours in the 2000 dataset. The temporal spectra obtained during 2001 are quite different from the results of the previous year. The modulations in the light curve are more noticeable and the temporal spectra present a higher number of modulation frequencies. One peculiar characteristic is the presence of a variable harmonic structure related to one of these modulation frequencies. This complex photometric behaviour may be explained by a more complicated unresolved combination of modulation frequencies, but more likely due to a combination of pulsations of the star plus modulations related to interaction with a close companion, maybe indicating a disc. However, these characteristics cannot be confirmed from single site observations. The complex and variable behaviour of NGC 246 needs the WET co-operation in order to completely resolve its light curve.

scholarly journals Light Curve Models for SN 1987A and Diagnosis of Supernova Interior

1988 ◽  
Vol 108 ◽  
pp. 319-334
Author(s):  
Ken’ichi Nomoto ◽  
Toshikazu Shigeyama ◽  
Masa-aki Hashimoto
Keyword(s):  
Light Curve ◽  
Reasonable Agreement ◽  
Light Curves ◽  
Shock Propagation ◽  
Helium Abundance ◽  
X Ray ◽  
Sn 1987A ◽  
Shock Heating ◽  
Helium Stars ◽  
Optical Light Curve

AbstractPresupernova evolution of the progenitor of SN 1987A, hydrodynamics of explosion (shock propagation, explosive nucleosynthesis), optical light curve due to shock heating and 56Co decay, and X-ray and γ-ray light curves are calculated and compared with the observations of SN 1987A. Constraints on the mass of the hydrogen-rich envelope Menv (i.e., mass loss history) and the helium abundance in the envelope are obtained from the progenitor’s blue-red-blue evolution as well as from the light curve. The explosion energy E and the mass and distribution of 56Ni are inferred from the light curves. Models and observations are in reasonable agreement for E/Menv = 1.5 ± 0.5 × 1050 erg/M⊙, Menv = 5 - 10 M⊙, and MNi ∼ 0.07 M⊙. Mixing of 56Ni into the envelope is indicated.Light curves of exploding bare helium stars are also calculated to see whether the observed Type Ib supernova light curves can be accounted for.

scholarly journals TT Arietis: 40 yr of photometry

2019 ◽  
Vol 489 (2) ◽  
pp. 2961-2975 ◽  
Author(s):  
Albert Bruch
Keyword(s):  
Time Scales ◽  
Orbital Period ◽  
Primary Component ◽  
Photometric Data ◽  
Light Curves ◽  
Average Period ◽  
High State ◽  
Periodic Oscillations ◽  
First Time ◽  
Tt Ari

ABSTRACT In an effort to characterize variations on the time-scale of hours and smaller during the high and low states of the nova-like variable TT Ari, light curves taken over the course of more than 40 yr are analysed. It is found that the well-known negative superhump observed during the high state persists until the present day at an average period of 0.132 95 d, which is slightly variable from year to year and exhibits substantial amplitude changes. The beat period between superhump and orbital period is also seen. Quasi-periodic oscillations occur at a preferred quasi-period of 18–25 min and undergo a systematic frequency evolution during a night. The available data permit for the first time a detailed investigation of the low state that is highly structured on time-scales of tens of days. On hourly time-scales, the light curve exhibits strong variations that are mostly irregular. However, during an interval of several days at the start of the low state, coherent 1.2 mag oscillations with a period of 8.90 h are seen. During the deep low state, quiet phases and strong (1.5–3 mag), highly structured flares alternate in irregular intervals of roughly 1 d. The quiet phases are modulated on the orbital period of TT Ari, suggesting reflection of the light of the primary component off the secondary. This is the first time that the orbital period is seen in photometric data.

scholarly journals BVRcIc Observations and Analysis of the Near-Contact Solar Type Eclipsing Binary, V530 Andromedae

2013 ◽  
Vol 2013 ◽  
pp. 1-8
Author(s):  
Ronald G. Samec ◽  
Daniel Flaaten ◽  
James Kring ◽  
Danny R. Faulkner
Keyword(s):  
Light Curve ◽  
Undergraduate Research ◽  
Initial Period ◽  
Light Curves ◽  
Eclipsing Binary ◽  
Massive Component ◽  
Solar Type ◽  
First Time ◽  
Curve Solution ◽  
Light Curve Solution

We present the first precision UBVRcIc light curves, an initial period study, and a simultaneous light curve solution for the near-contact solar type eclipsing binary V530 And. Our observations were taken with the 0.81 m Lowell reflector on 27 and 29 September, 2011, with time being granted from the National Undergraduate Research Observatory (NURO). Our Wilson Devinney Program solution yields a semidetached, V1010 Oph configuration: the more massive component is filling its Roche lobe. The system is apparently approaching contact for the first time. It is not a classic Algol.

scholarly journals The dual nature of blazar fast variability: Space and ground observations of S5 0716+714

2020 ◽  
Vol 501 (1) ◽  
pp. 1100-1115
Author(s):  
C M Raiteri ◽  
M Villata ◽  
D Carosati ◽  
E Benítez ◽  
S O Kurtanidze ◽  
...  
Keyword(s):  
Light Curve ◽  
Time Scales ◽  
Light Curves ◽  
Spectral Variability ◽  
Short Term ◽  
Dual Nature ◽  
X Ray ◽  
Geometric Origin ◽  
Optical Light Curve ◽  
Doppler Factor

ABSTRACT Blazar S5 0716+714 is well-known for its short-term variability, down to intraday time-scales. We here present the 2-min cadence optical light curve obtained by the TESS space telescope in 2019 December–2020 January and analyse the object fast variability with unprecedented sampling. Supporting observations by the Whole Earth Blazar Telescope Collaboration in B, V, R, and I bands allow us to investigate the spectral variability during the TESS pointing. The spectral analysis is further extended in frequency to the UV and X-ray bands with data from the Neil Gehrels Swift Observatory. We develop a new method to unveil the shortest optical variability time-scales. This is based on progressive de-trending of the TESS light curve by means of cubic spline interpolations through the binned fluxes, with decreasing time bins. The de-trended light curves are then analysed with classical tools for time-series analysis (periodogram, autocorrelation, and structure functions). The results show that below 3 d there are significant characteristic variability time-scales of about 1.7, 0.5, and 0.2 d. Variability on time-scales $\lesssim 0.2$ d is strongly chromatic and must be ascribed to intrinsic energetic processes involving emitting regions, likely jet substructures, with dimension less than about 10−3 pc. In contrast, flux changes on time-scales $\gtrsim 0.5$ d are quasi-achromatic and are probably due to Doppler factor changes of geometric origin.

scholarly journals Variability characteristics of Blazar 0J 287

1996 ◽  
Vol 175 ◽  
pp. 45-46
Author(s):  
L.O. Takalo ◽  
A. Sillanpää ◽  
T. Pursimo ◽  
H.J. Lehto ◽  
K. Nilsson ◽  
...  
Keyword(s):  
Light Curve ◽  
Time Scales ◽  
Light Curves ◽  
Data Archive ◽  
Extragalactic Object ◽  
Optical Light Curve ◽  
Blazar Oj 287

Blazar OJ 287 is one of the best observed extragalactic objects. It's historical light curve goes back to 1890′s. Based on the historical behaviour Sillanpää et al. (1988) showed that OJ 287 displays large periodic outbursts, with a period of 11.7 years. We have monitored OJ 287 intensively for two years, during the OJ-94 project. This project was created for monitoring OJ 287 during its predicted new outburst in 1994. In the data archive we have over 7000 observations on OJ 287, in the radio, infrared and optical bands. This data archive contains the best ever obtained light curves for any extragalactic object. The optical light curve shows continuous variability down to time scales of tens of minutes. The variability observed in OJ 287 can be broken down to (at least) four different categories:

scholarly journals Simultaneous Photometric and Spectroscopic Observations of the unusual Variable F-type stars HD 224638 and HD 224945.

1995 ◽  
Vol 155 ◽  
pp. 339-340 ◽  
Author(s):  
L. Mantegazza ◽  
E. Poretti ◽  
M. Bossi ◽  
F.M. Zerbi
Keyword(s):  
Time Scales ◽  
Spectral Type ◽  
Characteristic Frequency ◽  
Small Amplitude ◽  
Characteristic Time ◽  
Light Curves ◽  
Wave Shape ◽  
Spectroscopic Observations ◽  
New Class ◽  
Photometric And Spectroscopic Observations

The stars HD 224638 and HD 224945 belong to the new class of F0 V spectral type stars which show an unusual kind of variability for that region of the HR diagram (Mantegazza et al. 1993).The variability of these two stars has been discovered and studied by Mantegazza, Poretti & Zerbi (1994). They show small amplitude light variations with characteristic time scales of the order of one day. The light curves are not periodic and it is difficult to satisfactorily fit them even with several periodic terms.In order to explain our 1991 B colour observations we tentatively suggested that in both stars two close periodic terms were present with a characteristic frequency of about 0.8 c/d, and that these terms had a double wave shape for HD 224638 and a triple wave one for HD 224945.

scholarly journals What does FRB light-curve variability tell us about the emission mechanism?

2020 ◽  
Vol 498 (1) ◽  
pp. 651-664 ◽  
Author(s):  
Paz Beniamini ◽  
Pawan Kumar
Keyword(s):  
Light Curve ◽  
Time Scales ◽  
Production Efficiency ◽  
Compact Object ◽  
Light Curves ◽  
Radio Bursts ◽  
Intrinsic Variability ◽  
Temporal Correlations ◽  
Small Ratio ◽  
Powerful Radio Emission

ABSTRACT A few fast radio bursts’ (FRBs) light curves have exhibited large intrinsic modulations of their flux on extremely short ($t_{\rm r}\sim 10\, \mu$s) time-scales, compared to pulse durations (tFRB ∼ 1 ms). Light-curve variability time-scales, the small ratio of rise time of the flux to pulse duration, and the spectro-temporal correlations in the data constrain the compactness of the source and the mechanism responsible for the powerful radio emission. The constraints are strongest when radiation is produced far (≳1010 cm) from the compact object. We describe different physical set-ups that can account for the observed tr/tFRB ≪ 1 despite having large emission radii. The result is either a significant reduction in the radio production efficiency or distinct light-curve features that could be searched for in observed data. For the same class of models, we also show that due to high-latitude emission, if a flux f1(ν1) is observed at t1 then at a lower frequency ν2 < ν1 the flux should be at least (ν2/ν1)2f1 at a slightly later time (t2 = t1ν1/ν2) independent of the duration and spectrum of the emission in the comoving frame. These features can be tested, once light-curve modulations due to scintillation are accounted for. We provide the time-scales and coherence bandwidths of the latter for a range of possibilities regarding the physical screens and the scintillation regime. Finally, if future highly resolved FRB light curves are shown to have intrinsic variability extending down to ${\sim}\mu$s time-scales, this will provide strong evidence in favour of magnetospheric models.

Light curve analysis of six totally eclipsing W UMa binaries

2020 ◽  
Author(s):  
Olivera Latković ◽  
Atila Čeki
Keyword(s):  
Light Curve ◽  
Parameter Space ◽  
Curve Analysis ◽  
Light Curves ◽  
Evolutionary Status ◽  
Search Procedure ◽  
Light Curve Analysis ◽  
Short Period ◽  
Mass Ratios ◽  
First Time

Abstract We analyze multicolor light curves of six totally eclipsing, short-period W UMa binaries and derive, for the first time, their orbital and stellar parameters. The mass ratios are established robustly through an automated q-search procedure that performs an heuristic survey of the parameter space. Five stars belong to the W and one to the A subtype. The mass ratios range from 0.23 to 0.51 and the fillouts from $10\%$ to $15\%$. We estimate the ages and discuss the evolutionary status of these objects in comparison with a sample of other short-period W UMa binaries from the literature.

scholarly journals Flare Activity in the NGC 1275 Nucleus

1996 ◽  
Vol 171 ◽  
pp. 420-420 ◽  
Author(s):  
N.I. Merkulova ◽  
L.P. Metik
Keyword(s):  
Light Curve ◽  
Seyfert Galaxies ◽  
Crimean Astrophysical Observatory ◽  
Light Curves ◽  
Flare Activity ◽  
Different Types ◽  
Ngc 1275 ◽  
First Time

The simultaneous UBVRI – observations of some Seyfert galaxies have been carried out at Crimean Astrophysical Observatory using the 1.25m telescope. Photometric errors are less than 0.01 mag. By analysis of the NGC 1275 light curves within one night we are discovered at least two types of variability: 1) The flares with the maximal amplitudes of 5 – 30 % in the U-band and durations of 15 – 30 minutes. 2) For the first time we have found rapid red flares. For instance, the red flare on the light curve 22-23.10.1992 lasted ∼ 65 minutes (see Figure. Vertical axes are in magnitudes). The amplitude in the filter I is ∼ 25 % (top panel). The light curve in the U-band is on the bottom panel. Fluxes in the U,B,V-bands were almost constant. One can see the flux decreasing in some filters before this flare. We conclude, that light curve of NGC 1275 nucleus could be represented by a superposition of rapid flares of different types.

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