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S. V. Zharikov

Publications and source records attributed to S. V. Zharikov.

At least 55 records · Page 3Linked to original sources
arXiv2009

Toward Understanding The B[e] Phenomenon: III. Properties of the optical counterpart of IRAS 00470+6429

FS CMa type stars are a group of Galactic objects with the B[e] phenomenon. They exhibit strong emission-line spectra and infrared excesses, which are most likely due to recently formed circumstellar dust. The group content and identification criteria were described in the first two papers of the series. In this paper we report our spectroscopic and photometric observations of the optical counterpart of IRAS 00470+6429 obtained in 2003--2008. The optical spectrum is dominated by emission lines, most of which have P Cyg type profiles. We detected significant brightness variations, which may include a regular component, and variable spectral line profiles in both shape and position. The presence of a weak Li {\sc I} 6708 Åline in the spectrum suggests that the object is most likely a binary system with a B2--B3 spectral type primary companion of a luminosity $\log$ L/L$\odot$ = 3.9$\pm$0.3 and a late-type secondary companion. We estimate a distance toward the object to be 2.0$\pm$0.3 kpc from the Sun.

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arXiv2008

A likely optical counterpart of the G292.0+1.8 pulsar wind nebula

G292.0+1.8 is the Cas A-like supernova remnant containing the young pulsar PSR J1124-5916, which powers a compact torus-like pulsar wind nebula with a jet visible in X-rays. We have performed deep optical observations of the pulsar field to detect the optical counterpart of the pulsar and its nebula. The observations were carried out using the direct imaging mode of FORS2 at the ESO VLT/UT1 telescope in the V, R, and I bands. We also analyzed archival images obtained with the Chandra/ACIS-I, ACIS-S, and HRC-S in X-rays. In all three optical bands we detect a faint elliptical nebulosity, whose brightness peak and center position are consistent at a sub-arcsecond level with the X-ray position of the pulsar. The field is densely packed with background stars, but after subtraction of these stars the morphology of the object and the orientation of its major axis appear to be in a good agreement with the brightest inner part of the pulsar nebula torus region seen almost edge on in X-rays. Within the nebulosity we do not resolve any point-like optical object that could be identified with the pulsar and estimate its contribution to the observed nebulosity flux as <~20%. Extracting the X-ray spectrum from the physical region equivalent to the optical source position and extent and combining that with the measured optical fluxes, we compile a tentative multi-wavelength spectrum of the inner part of the nebula. Within uncertainties of the interstellar extinction towards G292.0+1.8 it is reminiscent of either the Crab or PSR B540-69 and J0205+6449 pulsar wind nebula spectra. The position, morphology, and spectral properties of the detected nebulosity suggest that it is the likely optical counterpart of the pulsar plus its wind nebula system in G292.0+1.8.

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arXiv2008

Cyclic brightening in the short-period WZ Sge-type cataclysmic variable SDSS J080434.20+510349.2

We have observed a new cataclysmic variable (CV) SDSS J080434.20+510349.2 and study the origin of a long-term variability found in its light curve. Multi-longitude time-resolved photometric observations were carried out to analyze the uncommon behavior also found recently in two newly discovered CVs. This study of SDSS J080434.20+510349.2 mainly concerns the understanding of the nature of the observed double-humped light curve and its relation to a cyclic brightening occurring during quiescence. The observations were obtained early in 2007, when the object was at about V~17.1, 0.4 mag brighter than the pre-outburst magnitude. The light curve shows a sinusoidal variability with an amplitude of about 0.07 mag and a periodicity of 42.48 min, which is half of the orbital period of the system. In addition, we have observed two "mini-outbursts" of the system up to 0.6 mag, with a duration of about 4 days each. The "mini-outburst" had a symmetric profile and repeated in about 32 days. Subsequent monitoring of the system shows a cyclical behaviour of such "mini-outbursts" with a similar recurrence period. The origin of the double-humped light curve and the periodic brightening is discussed in the light of the evolutionary state of SDSS J080434.20+510349.2.

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arXiv2007

Possible optical detection of a fast, nearby radio pulsar PSR B1133+16

Aims: We performed deep optical observations of the field of an old, fast-moving radio pulsar PSR B1133+16 in an attempt to detect its optical counterpart and a bow shock nebula. Methods: The observations were carried out using the direct imaging mode of FORS1 at the ESO VLT/UT1 telescope in the B, R, and H_alpha bands. We also used archival images of the same field obtained with the VLT in the B band and with the Chandra/ACIS in X-rays. Results: In the B band we detected a faint (B=28.1+/-0.3) source that may be the optical counterpart of PSR B1133+16, as it is positionally consistent with the radio pulsar and with the X-ray counterpart candidate published earlier. Its upper limit in the R band implies a color index B-R <0.5, which is compatible with the index values for most pulsars identified in the optical range. The derived optical luminosity and its ratio to the X-ray luminosity of the candidate are consistent with expected values derived from a sample of pulsars detected in both spectral domains. No Balmer bow shock was detected, implying a low density of ambient matter around the pulsar. However, in the X-ray and H_alpha images we found the signature of a trail extending ~4"-5" behind the pulsar and coinciding with the direction of its proper motion. If confirmed by deeper studies, this is the first time such a trail has been seen in the optical and X-ray wavelengths. Conclusions: Further observations at later epochs are necessary to confirm the identification of the pulsar by the candidate's proper motion measurements.

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arXiv2007

On the orbital period of the magnetic Cataclysmic Variable HS 0922+1333

Context: The object HS 0922+1333 was visited briefly in 2002 in a mini survey of low accretion rate polars (LARPs) in order to test if they undergo high luminosity states similar to ordinary polars. On the basis of that short observation the suspicion arose that the object might be an asynchronous polar (Tovmassian et al. 2004). The disparity between the presumed orbital and spin period appeared to be quite unusual. Aims: We performed follow-up observations of the object to resolve the problem. Methods: New simultaneous spectroscopic and photometric observations spanning several years allowed measurements of radial velocities of emission and absorption lines from the secondary star and brightness variations due to synchrotron emission from the primary. Results: New observations show that the object is actually synchronous and its orbital and spin period are equal to 4.04 hours. Conclusions: We identify the source of confusion of previous observations to be a high velocity component of emission line arousing from the stream of matter leaving L1 point.

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arXiv2006

Simultaneous photometry and echelle-spectroscopy of the dwarf nova BZ Ursae Majoris during the 2005 January Outburst

We report simultaneous photometric and echelle-spectroscopic observations of the dwarf nova BZ UMa during which we were lucky to catch the system at the onset of an outburst, the development of which we traced in detail from quiescence to early decline. The outburst had a precursor, and was of a short duration (~5 days) with a highly asymmetrical light curve. On the rise we observed a `jump' during which the brightness almost doubled over the course of half an hour. Power spectra analysis revealed well-defined oscillations with period of ~42 minutes. Using Doppler tomography we found that the unusual emission distribution detected in quiescence held during the outburst. After the maximum a new emission source arose, from the inner hemisphere of the secondary star, which became the brightest at that time. We analyse this outburst in terms of `inside-out' and `outside-in' types, in order to determine which of these types occured in BZ UMa.

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arXiv2005

Time-resolved observations of the short period CV SDSS J123813.73-033933.0

We observed a new and poorly studied cataclysmic variable (CV) SDSS J123813.73-033933.0 to determine its classification and binary parameters. Simultaneous time-resolved photometric and spectroscopic observations were carried out to conduct period analysis and Doppler tomography mapping. From radial velocity measurements of the Ha line we determined its orbital period to be 0.05592+/-0.00035$ days (80.53min). This period is longer than the first estimate of 76 min by Szkody et al. (2003), but still at the very edge of the period limit for hydrogen-rich CVs. The spectrum shows double-peaked Balmer emission lines flanked by strong broad Balmer absorption, indicating a dominant contribution by the white dwarf primary star, and is similar to the spectra of short-period low-mass transfer WZ Sge-like systems. The photometric light curve shows complex variability. The system undergoes cyclic brightening up to 0.4 mags, which are of semi-periodic nature with periods of the order of 8-12 hours. We also detect a 40.25 min variability of ~0.15 mag corresponding to half of the orbital period. Amplitude of the latter increases with the cyclic brightening of the system. We discuss the variable accretion rate and its impact on the hot spot as the most probable reason for both observed processes. SDSS J123813.73-033933.0 is preliminary classified as a WZ Sge-like short period system with low and unstable accretion rate.

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arXiv2005

Steps towards a solution of the FS Aurigae puzzle. I. Multicolour high-speed photometry with ULTRACAM

We present the analysis of high-speed photometric observations of FS Aur taken with the 4.2-m William Herschel Telescope and the high-speed camera ULTRACAM in late 2003. These observations were intended to determine whether there was any evidence of photometric variability with a period in the range 50-100 seconds. The discovery of such variations would help to explain existence, in FS Aur, of the very coherent photometric period of 205.5 min that exceeds the spectroscopic period by 2.4 times. Such a discrepancy in the photometric and spectroscopic periods is an unusual for a low mass binary system that is unambiguously identified as a Cataclysmic Variable. Using various methods, including wavelet-analysis, we found that with exception of the 205.5-minute periodicity, the main characteristic of variability of FS Aur is usual flickering and Quasi-Periodic Oscillations. However, we detected variability with a period of ~101 and/or ~105 sec, seen for a short time every half of the orbital period. These oscillations may be associated with the spin period of the white dwarf, not ruling out the possibility that we are observing a precessing rapidly rotating white dwarf in FS Aur.

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arXiv2004

Time-resolved observations of the short period CV SDSS J123813.73-033933

We present simultaneous spectral and photometric observations of SDSS J123813.73-033933.0. From Ha radial velocity measurements we determined the orbital period of the system to be 0.05592+/-0.00002 days (80.53 min). The spectrum shows double Balmer emission lines flanked by strong, broad absorption, indicating a dominant contribution from the white dwarf. The photometric light curve shows complex variability. The system undergoes cyclic brightening up to 0.4 mag which are semi-periodical on short time scales with periods of the order of 7-12 hours. We also detect 40.25 min variability (~0.15 mag) in the light curve, that corresponds to half the orbital period. Its amplitude increases with the cyclic brightening of the system.

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arXiv2002

A new two-pole accretion polar: RX J1846.9+5538

We report the discovery of a new, bright (V = 17 mag) AM Her system as the optical counterpart of the soft ROSAT All-Sky-Survey source RX J1846.9+5538 (= 1RXS J184659.4+553834). Optical photometric and spectroscopic follow-up observations reveal a single period of 128.7 min, consistent with a high degree of spin-orbit synchronization, and a low polar field strength ($B<20$ MG) of the primary accretion region. The system was observed in optical intermediate and high states that differ by about 1 mag. These brightness variations were accompanied by a correlated change of the optical light curve, which we interpret as a switch between one- and two-pole accretion. This explanation is also supported by the X-ray light curves, which at two different epochs display emission from two equally bright accretion regions separated by 160 degrees. Both spots possess distinct spectral X-ray properties as seen from the X-ray hardness ratio, where the secondary accretion region appears significantly softer, thus probably indicating a higher field strength compared to the primary region. In all ROSAT pointings a deep dip is present during the primary flux maxima, very likely caused by absorption in one of the accretion streams.

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arXiv2002

Subaru optical observations of the old pulsar PSR B0950+08

We report the B band optical observations of an old (17.5 Myr) radiopulsar PSR B0950+08 obtained with the Suprime-Cam at the Subaru telescope. We detected a faint object, B=27.07(16). Within our astrometrical accuracy it coincides with the radio position of the pulsar and with the object detected earlier by Pavlov et al. (1996) in UV with the HST/FOC/F130LP. The positional coincidence and spectral properties of the object suggest that it is the optical counterpart of PSR B0950+08. Its flux in the B band is two times higher than one would expect from the suggested earlier Rayleigh-Jeans interpretation of the only available HST observations in the adjacent F130LP band. Based on the B and F130LP photometry of the suggested counterpart and on the available X-ray data we argue in favour of nonthermal origin of the broad-band optical spectrum of PSR B0950+08, as it is observed for the optical emission of the younger, middle-aged pulsars PSR B0656+14 and Geminga. At the same time, the optical efficiency of PSR B0950+08, estimated from its spin-down power and the detected optical flux, is by several orders of magnitude higher than for these pulsars, and comparable with that for the much younger and more energetic Crab pulsar. We cannot exclude the presence of a compact, about 1'', faint pulsar nebula around PSR B0950+08, elongated perpendicular to the vector of its proper motion, unless it is not a projection of a faint extended object on the pulsar position.

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arXiv2001

The New AM Her System RX J0704.2+6203. Northern Twin of BL Hyi

We report here on the identification and study of the optical counterpart of the ROSAT source RX J0704.2+6203. Extensive spectral and photometric observation showed that the object belongs to the class of magnetic Cataclysmic Variables. We determined the orbital period of the system to be 97.27m and estimated the strength of its magnetic field to be on the order of 20 MG. The system was observed in both high and low states, common for its class. Other parameters of the magnetic close binary system were estimated. The spectral and photometric behavior of the object is similar to that of the well studied polar BL Hyi.

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arXiv2001

The new cataclysmic variable RX J1554.2+2721 in the period gap

We report on the results of a spectroscopic and photometric study of a new cataclysmic variable, identified as optical counterpart of the X-ray source RX J1554.2+2721 detected by ROSAT. The spectroscopic observations of the relatively bright (~16.5mag) object show systematic radial velocity variations with a semi-amplitude of ~140 km/sec. Besides the clear presence of distinct low and high states there are periodic photometric light variations with an amplitude of about 0.15 magnitude in the R band. The orbital period is 2.753h thus being within the period gap, at its upper border. The flux distribution in the spectrum of the object shows a substantial contribution of a M4V secondary, and also bears clear signs of cyclotron emission. Thus, we classify the discovered object as a new member of the AM Her class of magnetic cataclysmic variables. This classification is further supported by the soft X-ray spectrum, the characteristic profiles of the emission lines, the tomography map and the shape of the orbital light curve. A simple fitting of the spectrum in the low and high states suggests a reduced mass transfer rate in RX J1554.2+2721, compared to similar objects outside the period gap.

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arXiv2000

Optical photometry of the PSR B0656+14 and its neighborhood

We present the results of the broad-band photometry of the nearby middle-aged radio pulsar PSR B0656+14 and its neighborhood obtained with the 6-meter telescope of the SAO RAS and with the Hubble Space Telescope. The broad-band spectral flux $F_ν$ of the pulsar decreases with increasing frequency in the near-IR range and increases with frequency in the near-UV range. The increase towards UV can be naturally interpreted as the Rayleigh-Jeans tail of the soft thermal component of the X-ray spectrum emitted from the surface of the cooling neutron star. Continuation of the power-law component, which dominates in the high-energy tail of the X-ray spectrum, to the IR-optical-UV frequencies is consistent with the observed fluxes. This suggests that the non-thermal pulsar radiation may be of the same origin in a broad frequency range from IR to hard X-rays. We also studied 4 objects detected in the pulsar's 5" neighborhood.

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arXiv1999

BVR_cI_c light curves of GRB970508 optical remnant and magnitudes of underlying host galaxy

The observations with the SAO-RAS 6-m telescope in July-August 1998 show that the GRB970508 optical remnant has varied very little since November 1997. We can conclude that we observe a proper host galaxy without the GRB optical remnant. The fitting results of the light curve of the GRB remnant plus the host galaxy until about 400 days after the primary event are reported here. The best $χ^2$-fits with a power law, for most of the filters used, are not acceptable. Some intrinsic variability of the GRB optical remnant fading is possible, which demands a more complex law presenting the largest multiband homogeneous data set from a single telescope.

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arXiv1998

Properties of the host galaxy of the gamma-ray burst 970508 and local star-forming galaxies

Late-time observations of GRB970508 with the SAO-RAS 6-m telescope in July-August 1998 show that the optical transient (OT) varies very little since November 1997. Here we report the $BVR_cI_c$ light-curves behaviour up to 470 days from the GRB occurence with independent $BVR_cI_c$ power-law fits. After ~=200 days the power-law decay has ceased and the OT contamination to the host galaxy flux is already less than the observational errors of the brightness estimates. Spectral energy distribution for the host galaxy alone (without OT) and comparison of its broad-band spectrum to the average continuum spectra of different Hubble types galaxies are shown. The best fits to the BVR_cI_c spectral energy distribution of the GRB host with local starburst galaxies are found for the blue compact S0 dwarf galaxy NGC1510, the Scd starburst HII galaxy NGC7793 and the blue compact galaxy Mrk 1267. Position of the host galaxy in the M_B vs. log(D_25) diagram for local late-type LEDA galaxies allows us to attribute GRB970508 host galaxy to the blue compact galaxies.

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arXiv1998

BVR_cI_c light curves of GRB970508 optical remnant and colors of underlying host galaxy

Optical observations of the GRB 970508 optical remnant were continued with the 6-m telescope of SAO RAS in standard BVRcIc bands in Oct.-Dec.1997 and in Jan. 1998. The results of the photometry of GRB970508 remnant and of three nearby galaxies are presented. The BVRcIc light curves of the GRB970508 remnant may be described by a power law plus a constant F(t)=F_0(t-t_0)^α+C. In In parameters determination of the faint host galaxy we used the results of our BVRcIc photometry of May-August, 1997, the data of recent observations Keck-II and WHT telescopes and also the data of Rc and B bands photometry obtained by other authors based on our secondary standards. The level-off from the initial power-law decline seen in the first months after the burst observed in all bands. The effect is the most strong in Ic band. The best χ^2-fits for Fo, α, C parameters of the data in each of 4 bands point to the presence of a faint constant source with Ic=24.13\pm0.28, Rc = 25.55\pm0.19, V=25.80\pm 0.14, B=26.68\pm 0.14. The average αof light curve power law is -1.23\pm0.04. The optical remnant has the power law F_νν^βspectrum with spectral slope = -1.10\pm0.08 and does not change after optical curve maximum. BVRcIc spectrum together with an absolute magnitude of the constant component M_B_rest=-17.5\pm0.3 and the limit of the linear size of underlying host galaxy d<1.1 kpc, calculated for z=0.835,H_0=75km s^-1 Mpc^-1, q_0=0.5, correspond to a host galaxy, such as a starburst dwarf, red starburst dwarf, irregular dwarf, HII galaxy, or blue compact dwarf galaxy. All these types of dwarf galaxies show evidence of starburst or post starburst activity. Galaxy G2 has a spectrum similar to one of the host GRB galaxy and lies at the projected distance of ~20 kpc from GRB.

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