scholarly journals A systematic search for rapid photometric variability in southern symbiotic stars I. V648 Car

2012 ◽  
Vol 8 (S290) ◽  
pp. 179-180
Author(s):  
Rodolfo Angeloni ◽  
Francesco Di Mille ◽  
Carlos Eduardo Ferreira Lopes ◽  
Nicola Masetti
Keyword(s):  
Time Scales ◽  
Systematic Search ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
Small Class ◽  
Photometric Variability ◽  
X Ray ◽  
First Results ◽  
Over Time

AbstractWe present the first results from the systematic observational campaign aimed at studying rapid photometric variability (i.e., flickering) in southern symbiotic stars. In particular, we report on the discovery of strong flickering from V648Car (also known as SS73-17), a poorly studied system belonging to the small class of hard X-ray emitting symbiotic stars. To our knowledge, with a U-band flickering amplitude >0.6mag over time scales of minutes, it is one of the most significant flickering ever reported from a symbiotic star.

scholarly journals X-Ray and Ultraviolet Observations of AG Draconis during Quiescence and Outburst

1987 ◽  
Vol 93 ◽  
pp. 763-763
Author(s):  
A. Cassatella ◽  
F.A. Córdova ◽  
M. Friedjung ◽  
J. Kenyom ◽  
L. Piro ◽  
...  
Keyword(s):  
Orbital Motion ◽  
Uv Light ◽  
Low Energy ◽  
Emission Lines ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
Uv Spectrum ◽  
X Ray ◽  
High Ionization ◽  
Ultraviolet Observations

AbstractWe describe the first X-ray monitoring of a symbiotic star during phases of enhanced activity. AG Dra is a Pop II object with a composite spectrum, characterized by a cool K-type component, prominent high ionization emission lines and a strong UV continuum which is attributed to a hot dwarf companion. Periodic variability of the UV radiation during minimum could be attributed to the orbital motion of the system. In April 1980 HEAO-2 detected an intense, soft X-ray flux from AG Dra, stronger than in other symbiotic stars. After one major outburst of November 1980, which continued until 1983, two more outbursts occurred in February 1985 and January 1986, and coordinated X-ray (EXOSAT) and ultraviolet (IUE) observations were organized to study the behaviour of AG Dra during different activity phases. EXOSAT observations made during decline after the 1985 outburst, revealed a weak X-ray flux in the Thin Lexan filter of the Low Energy dedtector. Observations made during minimum, in June and November 1985, at phases 0.22 and 0.50 of the UV light curve, disclosed the presence of an intense X-ray flux, which was not occulted in November. AG Dra was again observed with EXOSAT in February 1986 when the stellar luminosity was still at maximum. No X-ray flux was detected, in spite of the prominent, high ionization UV spectrum observed with IUE.A detailed discussion of the X-ray and ultraviolet results on AG Dra in the light of possible models is in progress.

scholarly journals First Results of Optical Monitoring of 3C 390.3

1997 ◽  
Vol 159 ◽  
pp. 163-164
Author(s):  
M. Dietrich ◽  
P.T. O’Brien ◽  
K. M. Leighly
Keyword(s):  
Time Scales ◽  
Broad Band ◽  
Emission Lines ◽  
High Temporal Resolution ◽  
Line Profiles ◽  
X Ray ◽  
First Results ◽  
Long Time ◽  
Flux Measurements ◽  
Calar Alto

In late autumn 1994, the International AGN Watch started a multiwavelength monitoring campaign on 3C 390.3, the first radio-loud AGN to be selected for high temporal-resolution monitoring from the radio domain to X-ray energies. This AGN is is of particular interest since significant variations have been observed on both short and long time scales in both the line fluxes and line profiles (Barr et al. 1980, Veilleux & Zheng 1991).In the optical, spectroscopic data and broad-band flux measurements in B, V, R, and I were obtained. The brightness of 3C 390.3 was calculated relative to the stars in the field. The R magnitudes are based on observations recorded at Calar Alto, Spain, in 1994 December. Generally, AGN spectra are intercalibrated using narrow forbidden emission lines since these lines can be taken as constant on time scales of decades (Peterson 1993). Since the [O III] λλ4959, 5007 flux is variable on time scales of several months (Zheng et al. 1995), these lines were studied in detail. We found that they were constant within ~2% during 1995 (Dietrich et al. 1996). The spectra were therefore intercalibrated by using the narrow forbidden emission lines. 3C 390.3 was also observed with IUE for 14 months (O’Brien et al. 1996) and with ROSAT for nine months in 1995 (Leighly et al. 1996). Radio data were also obtained during a 3-month MERLIN campaign.

scholarly journals Understanding extreme quasar optical variability with CRTS – II. Changing-state quasars

2019 ◽  
Vol 491 (4) ◽  
pp. 4925-4948 ◽  
Author(s):  
Matthew J Graham ◽  
Nicholas P Ross ◽  
Daniel Stern ◽  
Andrew J Drake ◽  
Barry McKernan ◽  
...  
Keyword(s):  
Real Time ◽  
Time Scales ◽  
Systematic Search ◽  
Optical Variability ◽  
Photometric Variability ◽  
Mid Infrared ◽  
Spectroscopic Change

ABSTRACT We present the results of a systematic search for quasars in the Catalina Real-time Transient Survey exhibiting both strong photometric variability and spectroscopic variability over a decadal baseline. We identify 111 sources with specific patterns of optical and mid-infrared photometric behaviour and a defined spectroscopic change. These ‘changing-state’ quasars (CSQs) form a higher luminosity sample to complement existing sets of ‘changing-look’ AGNs and quasars in the literature. The CSQs (by selection) exhibit larger photometric variability than the changing-look quasars (CLQs). The spectroscopic variability is marginally stronger in the CSQs than CLQs as defined by the change in H β/[$\rm {O \,\rm {\small {III}}}$] ratio. We find 48 sources with declining H β flux and 63 sources with increasing H β flux, and discover 8 sources with $z$ > 0.8, further extending the redshift arm. Our CSQ sample compares to the literature CLQ objects in similar distributions of H β flux ratios and differential Eddington ratios between high (bright) and low (dim) states. Taken as a whole, we find that this population of extreme varying quasars is associated with changes in the Eddington ratio and the time-scales imply cooling/heating fronts propagating through the disc.

scholarly journals UV spectroscopy confirms SU Lyn to be a symbiotic star

2020 ◽  
Vol 500 (1) ◽  
pp. L12-L16
Author(s):  
Vipin Kumar ◽  
Mudit K Srivastava ◽  
Dipankar P K Banerjee ◽  
Vishal Joshi
Keyword(s):  
Near Infrared ◽  
Uv Spectroscopy ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
High Excitation ◽  
Uv Spectrum ◽  
Infrared Observations ◽  
X Ray ◽  
The Galaxy ◽  
Type Giant

ABSTRACT SU Lyn, a star that ostensibly appears to be an unremarkable late M type giant, has recently been proposed to be a symbiotic star largely based on its hard X-ray properties. The star does not display, in low-resolution optical spectra, the high excitation lines typically seen in the spectra of symbiotic stars. In this work, ultraviolet (UV), optical, and near-infrared observations are presented, aimed at exploring and strengthening the proposed symbiotic classification for this star. Our far-UV 1300–1800 Å spectrum of SU Lyn, obtained with the ASTROSAT mission’s UVIT payload, shows emission lines of Si iv, C iv, O iii, and N iii in a spectrum typical of symbiotic stars. The UV spectrum robustly confirms SU Lyn’s symbiotic nature. The detection of high excitation lines in a high-resolution optical spectrum further consolidates its symbiotic nature. As is being recognized, the potential existence of other similar symbiotic systems could significantly impact the census of symbiotic stars in the Galaxy.

First Results from a Systematic Search for New X-ray Pulsators in ROSAT PSPC Fields

1998 ◽  
pp. 411-417
Author(s):  
G. L. Israel ◽  
A. Treves ◽  
L. Stella ◽  
L. Angelini ◽  
N. E. White ◽  
...  
Keyword(s):  
Systematic Search ◽  
X Ray ◽  
First Results

On the long-term variability of high massive X-ray binary Cyg X-1

2018 ◽  
Vol 14 (S346) ◽  
pp. 206-211
Author(s):  
Eugenia Karitskaya ◽  
Nikolai Bochkarev ◽  
Vitalij Goranskij ◽  
Natalia Metlova
Keyword(s):  
Absorption Line ◽  
Time Scales ◽  
Photometric Variability ◽  
X Ray ◽  
Fundamental Parameters ◽  
Photometric Observations ◽  
Soft State ◽  
Depth Increase ◽  
Line Depth

Abstract. We continue our study of spectral and photometric variability of Cyg X-1 on the basis of the 45-year long series of multicolor photometric observations and many-year-long series of spectral observations we have accumulated up to now. The mean level of star brightness continues to decrease since 1999 with the variations on smaller time scales superimposed. There is a connection between X-ray and optical changes. The chaotic variations of X-ray flux sometimes reaching to “hard” - “soft” state irregular changes switch on when U brightness decrease and He I λ 4713 Å absorption line depth increase. And inversely - they switch off during U brightness increasing and He I λ 4713 Å absorption line depth decreasing. This may be connected with star size variations, causing outflow gas instability. It is concluded that the fundamental parameters of the supergiant in the system of Cyg X-1 continue to vary on the time scales of years - decades.

scholarly journals The nature of the symbiotic candidate 2MASS J07363415+6538548 in the field of NGC 2403

2020 ◽  
Vol 499 (2) ◽  
pp. 2116-2123
Author(s):  
J Merc ◽  
R Gális ◽  
J Kára ◽  
M Wolf ◽  
M Vrašťák
Keyword(s):  
Effective Temperature ◽  
Milky Way ◽  
Photometric Data ◽  
Cataclysmic Variable ◽  
X Rays ◽  
Symbiotic Star ◽  
Symbiotic Stars ◽  
Rotational Period ◽  
Online Database ◽  
X Ray

ABSTRACT New Online Database of Symbiotic Variables includes several poorly characterized objects and candidate symbiotic stars, not only in the Milky Way but also in other galaxies. The goal of the research presented in this paper was to reveal the nature of 2MASS J07363415+6538548, the object discovered as an X-ray source in the field of NGC 2403, and tentatively classified as a symbiotic candidate or a cataclysmic variable. By analysis of available photometric data from ground-based surveys, together with a high-precision photometry from TESS, remarkable astrometric measurements of the Gaia satellite and observations of other surveys spanning from X-rays to infrared, we have found that the object neither not a symbiotic star nor a cataclysmic variable, but rather an active K-type dwarf. The star is located in the distance of 415 pc, has an effective temperature of 4275 K, luminosity of 0.14 L⊙, mass of 0.7 M⊙, and radius of 0.7 R⊙. It has a rotational period ∼ 3 d and is a strong X-ray source with the X-ray luminosity of ∼ $10^{30}\rm \, erg\, s^{-1}$. Gyrochronology and isochrone fitting confirmed that the star is young.

scholarly journals Variability of L Dwarfs in the Near Infrared

2003 ◽  
Vol 211 ◽  
pp. 455-456 ◽  
Author(s):  
José A. Caballero ◽  
Víctor J. S. Béjar ◽  
Rafael Rebolo
Keyword(s):  
Time Scales ◽  
Near Infrared ◽  
Brown Dwarfs ◽  
L Dwarfs ◽  
Atmospheric Changes ◽  
Changes Over Time ◽  
Over Time

We have obtained series of images in the near infrared J and Ks bands for seven L-type dwarfs with a duration of 3 to 6 hours. We present results on: 1) the amplitude of variability associated with atmospheric changes over time scales from minutes to several hours; 2) the search for cool companions in wide orbits; 3) the search for transits of brown dwarfs and planetary companions in very close orbits.

scholarly journals From Femtoseconds to Hours–Measuring Dynamics over 18 Orders of Magnitude with Coherent X-rays

2021 ◽  
Vol 11 (13) ◽  
pp. 6179
Author(s):  
Felix Lehmkühler ◽  
Wojciech Roseker ◽  
Gerhard Grübel
Keyword(s):  
Time Scales ◽  
Free Electron Laser ◽  
Photon Correlation Spectroscopy ◽  
Signal To Noise Ratio ◽  
Coherent Scattering ◽  
Correlation Spectroscopy ◽  
X Rays ◽  
Photon Correlation ◽  
X Ray ◽  
Scattering Technique

X-ray photon correlation spectroscopy (XPCS) enables the study of sample dynamics between micrometer and atomic length scales. As a coherent scattering technique, it benefits from the increased brilliance of the next-generation synchrotron radiation and Free-Electron Laser (FEL) sources. In this article, we will introduce the XPCS concepts and review the latest developments of XPCS with special attention on the extension of accessible time scales to sub-μs and the application of XPCS at FELs. Furthermore, we will discuss future opportunities of XPCS and the related technique X-ray speckle visibility spectroscopy (XSVS) at new X-ray sources. Due to its particular signal-to-noise ratio, the time scales accessible by XPCS scale with the square of the coherent flux, allowing to dramatically extend its applications. This will soon enable studies over more than 18 orders of magnitude in time by XPCS and XSVS.

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