Short-Term Spectral Variability of γ^{2} Velorum. Photometric Observations

AbstractWe report on combined spectroscopic and photometric observations of EW Lac during its outburst of 1983. At this time the star’s Hα and Hβ lines showed strong doubled-peaked emission profiles which were variable with time. UBV photometry exhibited a long-term and frequent erratic short-term variations. The amplitude of U, B and V variations reached about 0.3 magnitude on October 15, 1983. Both Hβ emission and the structure of the shell absorption lines of the star also displayed anomalous behavior in 1983. It is evident that this star was in a strong active phase at that time.

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Optical variability of three extreme TeV blazars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1598 ◽

2020 ◽

Vol 496 (2) ◽

pp. 1430-1444

Author(s):

Ashwani Pandey ◽

Alok C Gupta ◽

G Damljanovic ◽

P J Wiita ◽

O Vince ◽

...

Keyword(s):

Time Scales ◽

Spectral Energy ◽

Spectral Variability ◽

Weighted Mean ◽

Energy Distributions ◽

Optical Telescope ◽

Physical Mechanisms ◽

Photometric Observations ◽

All Optical ◽

The One

ABSTRACT We present the results of optical photometric observations of three extreme TeV blazars, 1ES 0229+200, 1ES 0414+009, and 1ES 2344+514, taken with two telescopes (1.3 m Devasthal Fast Optical Telescope, and 1.04 m Sampuranand Telescope) in India and two (1.4 m Milanković telescope and 60 cm Nedeljković telescope) in Serbia during 2013–2019. We investigated their flux and spectral variability on diverse time-scales. We examined a total of 36 intraday R-band light curves of these blazars for flux variations using the power-enhanced F-test and the nested ANOVA test. No significant intraday variation was detected on 35 nights, and during the one positive detection the amplitude of variability was only 2.26 per cent. On yearly time-scales, all three blazars showed clear flux variations in all optical wavebands. The weighted mean optical spectral index (αBR), calculated using B − R colour indices, for 1ES 0229+200 was 2.09 ± 0.01. We also estimated the weighted mean optical spectral indices of 0.67 ± 0.01 and 1.37 ± 0.01 for 1ES 0414+009, and 1ES 2344+514, respectively, by fitting a single power law (Fν ∝ ν−α) in their optical (VRI) spectral energy distributions. A bluer-when-brighter trend was only detected in the blazar 1ES 0414+009. We briefly discuss different possible physical mechanisms responsible for the observed flux and spectral changes in these blazars on diverse time-scales.

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Circular Polarimetry of AM Herculis

International Astronomical Union Colloquium ◽

10.1017/s0252921100090333 ◽

1983 ◽

Vol 72 ◽

pp. 207-210

Author(s):

V. Piirola ◽

O. Vilhu ◽

I. Tuominen

Keyword(s):

Circular Polarization ◽

Magnetic Axis ◽

Light Curves ◽

Short Term ◽

Probable Explanation ◽

Photometric Observations ◽

Peak Value

ABSTRACTCircular polarimetry in the red and simultaneous photometric observations in the UBVRI bands during the period June 1-3, 1981, are discussed. The peak value of negative circular polarization PV ~ -15 % is stronger than observed in 1976-79. Variations in the shape of the polarization and light curves occur from night to night. The positive crossover and reversal of the sign of the circular polarization are only marginal. A probable explanation of the short term variations seems to be the changing shape and position of the accretion columns with respect to the magnetic axis

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REVISITING THE SHORT-TERM X-RAY SPECTRAL VARIABILITY OF NGC 4151 WITHCHANDRA

The Astrophysical Journal ◽

10.1088/0004-637x/714/2/1497 ◽

2010 ◽

Vol 714 (2) ◽

pp. 1497-1510 ◽

Cited By ~ 16

Author(s):

Junfeng Wang ◽

G. Risaliti ◽

G. Fabbiano ◽

M. Elvis ◽

A. Zezas ◽

...

Keyword(s):

Spectral Variability ◽

Short Term ◽

X Ray ◽

Ngc 4151

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Recent UBVR Photometry of Symbiotic Stars

Open Astronomy ◽

10.1515/astro-2017-0095 ◽

2003 ◽

Vol 12 (4) ◽

Author(s):

A. Skopal ◽

M. Vaňko ◽

T. Pribulla ◽

D. Chochol

Keyword(s):

Light Curve ◽

Active Phase ◽

Symbiotic Stars ◽

Short Term ◽

Quiescent Phase ◽

Photometric Observations ◽

Made In

AbstractWe present recent photometric observations of Z And, BF Cyg, and AX Per made in the standard Johnson UBVR system. The main characteristics of their light behavior can be summarized as follows: Z And: our observations cover the recent active phase, from its maximum in 2000 December to the latest measurements (2003 September). BF Cyg: the minimum of the recent wave in the star’s brightness was the deepest ever observed; in 2003 February a short-term flare developed in the light curve. AX Per: from 1995 October the light curve displays signatures of a quiescent phase of the star; in 2003 May a 0.5 mag flare was detected.

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Short-Term Spectral Variability of the Herbig Ae/Be Star HD37806

Astrophysics ◽

10.1007/s10511-019-09560-z ◽

2019 ◽

Vol 62 (1) ◽

pp. 18-34

Author(s):

M. A. Pogodin ◽

O. V. Kozlova ◽

I. Yu. Alekseev ◽

S. E. Pavlovskiy

Keyword(s):

Spectral Variability ◽

Short Term ◽

Be Star

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Let there be more variability in two γ Cas stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa617 ◽

2020 ◽

Vol 494 (1) ◽

pp. 958-974 ◽

Cited By ~ 2

Author(s):

Yaël Nazé ◽

Andrzej Pigulski ◽

Gregor Rauw ◽

Myron A Smith

Keyword(s):

Spectroscopic Analysis ◽

Activity Levels ◽

Be Stars ◽

Spectral Variability ◽

Short Term ◽

Photometric Variability ◽

High Frequencies ◽

Low Amplitude ◽

High Degree

ABSTRACT We investigate the short-term optical variability of two γ Cas analogues, πAqr and BZ Cru, thanks to intensive ground-based spectroscopic and space-borne photometric monitorings. For both stars, low-amplitude (mmag) coherent photometric variability is detected. The associated signals display long-term amplitude variations, as in other Be stars. However, these signals appear at high frequencies, especially in πAqr, indicating p modes with a high degree l, a quite unusual feature amongst Be stars. While BZ Cru presents only low-level spectral variability, without clear periodicity, this is not the case of πAqr. In this star, the dominant photometric frequencies, near ∼12 d−1, are confirmed spectroscopically in separate monitorings taken during very different disc activity levels; the spectroscopic analysis suggests a probable tesseral nature for the mode.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3561 ◽

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.

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