Dmitry Shakhovskoy

• PhD
• Senior Researcher at Crimean Astrophysical Observatory

We report the discovery of mid-infrared excess emission in the young object RZ Psc. The excess constitutes ~8% of its Lbol and is well fit by a single 500 K blackbody, implying a dust-free region within ~0.7 AU for optically thick dust. The object displays dust obscuration events (UXOR behaviour) on a time scale that suggests dusty material on orbi...

The classical Herbig Ae/Be (HAeBe) star RR Tau is known as a highly variable young star with an amplitude of variability of about 4mag in the V pass-band. In this paper we present the results of coordinated Crimea-Dodaira multi-band photo-polarimetric observations of this star which cover fully the observed interval of its brightness changes. Withi...

We present new results of observations of the 6708 Ä line in twelve CP stars made with three telescopes: the ESO CAT telescope, the Crimean Observatory (CrAO) 2.6-m telescope, and the Nordic Optical Telescope (NOT). Unique profile and wavelength variations of the line at 6708 Ä were discovered in two stars, HD 60435 and HD 83368. We present argumen...

This paper continues a study of the photometric activity of UX Ori stars in the optical and near-infrared (JHKLM bands) initiated in 2000. For comparison, the list of program stars contains two Herbig Ae stars that are photometrically quiet in the optical: MWC480 andHD179218. Fadings ofUXOri stars in the optical (V band) due to sporadic increases o...

We present results of polarimetric observations of Saturn's moon Enceladus carried out from April 14, 2010 to April 13, 2013 in WR spectral band (550-750 nm). We used 2.6-m telescope equipped with a one-channel photoelectric photometer-polarimeter (Crimean Astrophysical Observatory). The measurements were performed at phase angles ranging from 1.65...

We present results of a multisite photometric campaign on the high-amplitude δ Scuti star KIC 6382916 in the Kepler field. The star was observed over a 85-d interval at five different sites in North America and Europe during 2011. Kepler photometry and ground-based multicolour light curves of KIC 6382916 are used to investigate the pulsational cont...

We present results of a multi-site photometric campaign on the high-amplitude $\delta$\,Scuti star KIC\,6382916 in the {\it Kepler} field. The star was observed over a 85-d interval at five different sites in North America and Europe during 2011. {\it Kepler} photometry and ground-based multicolour light curves of KIC\,6382916 are used to investiga...

[Abridged] Context. To construct and interpret the spectral energy distribution (SED) of BL Lacertae objects, simultaneous broad-band observations are mandatory. Aims. We present the results of a dedicated multi-wavelength study of the high-frequency peaked BL Lacertae (HBL) object and known TeV emitter 1ES 2344+514 by means of a pre-organised camp...

It is well known that atmospheric aerosols strongly affect the terrestrial climate and environment, their climatic effects being comparable to those of the greenhouse gases. However accurate quantitative estimates of these effects and, especially, of their anthropogenic components are absent, thereby making it difficult to formulate scientifically...

In a prolonged study (about 30 years) of the photometric activity of WW Vul we have discovered unusual eclipses in the light curve of this star. They last 2-3 years and repeat with a period of 13.9 years. One nontrivial feature of these eclipses is that in their deepest part the star’s brightness increases. Changes in the color indices during these...

We have analyzed the activity of four UX Ori stars in the near-IR (JHKL) and visual (V) using the results of long-term photometric observations. For comparison, we also obtained IR (JHKLM) photometric observations of two visually quiet young stars of close spectral types (AB Aur and HD 190073). For the photometrically most active UX Ori stars BF Or...

We present ground-based and HST optical observations of the optical transients (OTs) of long-duration Gamma Ray Bursts (GRBs) 060729 and 090618, both at a redshift of z = 0.54. For GRB 060729, bumps are seen in the optical light curves (LCs), and the late-time broadband spectral energy distributions (SEDs) of the OT resemble those of local type Ic...

We present moderate-resolution optical spectra of the highly variable Herbig Ae star RR Tauri over 12 epochs spanning ~2.5 mag in V. Combining normalized spectra with contemporaneous photometry from two databases, we analyze both equivalent width and flux behavior as a function of system brightness for lines from the Ca II K line in the blue to the...

We present the results of long term optical monitoring of known and candidate TeV Blazars. These observations were obtained with the 0.6m telescope at the Bell Observatory of Western Kentucky University and the 1.3M AZT11 telescope at the Crimean Astrophysical Observatory. A total of 10 known TeV Blazars and 11 TeV Blazar candidates are being monit...

Results from simultaneous spectral and photometric monitoring of the Herbig Ae star CQ Tau in the neighborhood of the Hα and resonance sodium doublet Na I D lines are presented. It is shown that the inner structure of the accretion disk of CQ Tau is nonuniform and consists of two regions with quite different kinematic characteristics. Region I is c...

We present the results of simultaneous UBVRI photometry and polarimetry of the classical T Tauri star CO Ori carried out at the Crimean Astrophysical Observatory during the 18 years between 1986 and 2004. We show that the variations of linear polarization accompanying the star’s brightness variations follow the law characteristic of UX Ori stars. T...

The results of the high-resolution long-term spectral monitoring of the Herbig Ae star HD 31648 in the regions of emission Hα line, Na I D resonance lines and OI 7774 lines are presented. We confirmed the conclusion, made in previous papers, that the spectral variability of the star in the region of Hα line have a cyclic character. It is manifeste...

Results of simultaneous spectral and photometric monitoring of the Ae Herbig star WW Vul in the neighborhoods of the Ha line and the sodium NaI D resonance doublet are reported. It is shown that the spectral variability of the star is caused mainly by the anisotropic disk wind, whose high velocity component forms in the inner region of the accretio...

We present the results of multi-year photometric and polarimetric observations of the young binary system DF Tau in the UBVRI bands, as well as bispectrum speckle interferometric observations in the $H$ and $K$ bands obtained between 2001 and 2003. The photometric and polarimetric observations suggest that the linear polarization of DF Tau does not...

We present the results of polarimetric and photometric observations of dynamically new comet C/2002 T7 (LINEAR) at phase angles from 6° to 26°. During the observations, the comet was at a distance of 2.7–1.3 AU from the Sun and 1.7–2.0 AU from the Earth. The aperture polarimetry was made with the 2.6-m Shain telescope and the 1.25-m AZT-11 telescop...

Photometric and polarimetric observations of DF Tau were carried out between 1991 and 1998 using the five-band photopolarimeter mounted at the 1.25m telescope of the Crimean Astrophysical Observatory (CrAO). This instrument permits simultaneous observations of polarization and brightness in the U, B, V, R, and I bands. The effective wavelengths of...

We present results of imaging and aperture polarimetry of the dust of comet 2P/Encke at phase angles 91–105$^{\circ}$, obtained during the 2003 apparition. We investigate how strongly molecular emissions transmitted by the filters used in the observations can affect the resulting polarization of cometary dust. This problem is of particular importan...

An historical light curve for the UX Ori star CQ Tau is constructed for the period from 1939 through 2003. The star’s photometric behavior includes a cyclical component with a period of about 21 years. An analysis of the periodogram reveals a shorter cycle with a duration of about 1020 days after this cycle is subtracted. Since the photometric acti...

A program of Many-sites Multi Channel simultaneous observations of flare stars by a network of telescops was initiated in 1998. The purpose of this program is to investigate the fine structure of the flares light-curve in UBVRI, depressing atmospheric and instrumental noises. In this paper we present the results of the observations on the Flare sta...

We present the results of our simultaneous photometric and polarimetric observations of the Herbig Ae/Be star VX Cas acquired in 1987–2001. The star belongs to the UX Ori subtype of young variable stars and exhibits a rather low level of photometric activity: only six Algol-like minima with amplitudes ΔV>1m were recorded in 15 years of observations...

We present the results of synchronous photometric and polarimetric U BV RI observations of the irregular variable star RZ Psc, acquired at the Crimean Astrophysical Observatory in 1989–2002. The star’s photometric behavior is characterized by short, sporadic Algol-like dimmings. We observed only one deep minimum, with a V amplitude of about 1.5m, d...

Echelle spectrograms of the flaring red dwarf EV Lac obtained on the Nordic Optical Telescope are used to study the chromosphere of the star during the impulsive flare of 23:19 UT on August 30, 1994, and in two nearby time intervals when UBV RI photometry showed the star to be in a quiescent state. The high spectral resolution of the observations e...

In the course of photopolarimetric monitoring of the Herbig Ae star WW Vul, an unusual variation of linear polarization upon energence from a deep minimum was recorded, which cannot be explained by the standard mechanism for such objects (UX Ori stars): a variable contribution of radiation scattered by circumstellar dust. An analysis of possible ca...

We present observations of the UX Ori star RR Tau in the optical (UBVRI)and near infrared (JHKLM)acquired between November 2000 and April 2001. We recorded a uniquely long (about half a year) Algol-like minimum with an amplitude of ΔV≈2.9. The dimming of RR Tau was accompanied by an increase of the linear polarization, typical of UX Ori stars and t...

Observations of the brightness, color, and polarization of the fuor V1057 Cyg over more than 30 years are presented and briefly discussed. Variability of the linear polarization was found.

We present in this paper several high resolution (R = 27 000) spectra of five UXORs (UX Ori, CQ Tau, BF Ori, RR Tau, WW Vul), which cover the entire visual range, from 3900 to about 8700 Å. There are between 4 and 7 spectra per star, obtained over a time interval of two years. Simultaneous or quasi-simultaneous photometric observations were also ob...

UBVRI observations of circular polarization in WW Vul are presented. A positive polarization of ∼0.1% was detected with a signal-to-noise ratio from 3 to 5 in each of the bands and more than 5 when averaged over all five bands. This observed polarization roughly corresponds to a 1% circular polarization of the radiation scattered in a circumstellar...

We present equivalent widths and profiles for H-alpha, H-beta, H-gamma and He I lambda 4471 Angstrom emission lines obtained in observations of the flares of EV Lac made at the Crimean Astrophysical Observatory in 1994 and 1995. Our semi-empirical modeling of the flares gives insight into the structure of the emitting regions, including a temperatu...

We present the results of our long-term photometric and polarimetric observations of the classical Herbig Ae star VV Ser, performed at the Crimean Astrophysical Observatory as part of a program of photometric and polarimetric monitoring of UX Ori stars. We recorded an unusually deep minimum of VV Ser (ΔV≈3m), with a turn of the color tracks in the...

We present spectral observations of the red-dwarf flare star EV Lac made at the Crimean Astrophysical Observatory in 1994 and 1995, and describe a method for semi-empirical modeling of the chromospheres of red dwarfs based on their emission spectra. We have modeled the quiescent state of the chromosphere of EV Lac for the cases of a homogeneous chr...

We present moderate resolution optical spectra of the highly variable Herbig Ae star RR Tau over 12 epochs spanning 2.5 magnitudes in V. The data cover most of the optical spectrum from the CaII K line in the blue to the CaII infrared triplet in the far red. Using contemporaneous photometric measurements from two sources, we have reliable estimates...

Many-site multichannel simultaneous observations of the flare star EV Lac revealed high-frequency brightness oscillations superimposed on the mean flare light curve. Oscillations occur at the earliest stage of a flare and are visible during the high state. Coherent oscillations of 26 and 13 sec were seen during three flare events. The pulsed fracti...

Regular photometric observations of the two active flare stars EV Lac and AD Leo were carried out in 1996–1999. We have compared the location of the intrinsic radiation of the strongest flares in UBVRI two-color diagrams with those predicted by various models for the radiation sources. Our statistical analysis of flares in EV Lac confirms the 7.5-y...

Photopolarimetry of the classic Herbig Ae star VV Ser was carried out at the Crimean Astrophysical Observatory as a part of the longterm program of UX Ori type stars monitoring. An exceptionally deep minimum, down to V = 14m8, was observed in 1998. For the first time for this star the “blueing effect” was detected in U - B and B - V color indexes....

During spectral observations of the flare red dwarf star EV Lac, carried out at the 2.6-m Shajn reflector, emission profiles of the hydrogen and helium lines have been registered both for the quiet state of the star and for flares. Using the Crimean computation algorithm, the hydrostatic models have been calculated for a homogeneous stellar chromos...

Observations of the polarization of stars in the direction of a molecular cloud in Serpens are presented. A dependence of the degree of linear polarization on total absorption Av is found in their direction, different for stars in the cloud and in its vicinity. On this basis, it is concluded that the polarizing efficiency of particles in the cloud...

We present the results of simultaneous UBVRI photometric and polarimetric observations of the Ae Herbig star SV Cep made in 1987–1998. Over these 11 years, only a single deep (ΔV>1m) brightness minimum was observed. Near this minimum, the brightness decrease was accompanied by an increase of the linear polarization, as is typical of young UX Ori st...

In this paper we summarize the results of our analysis of the long-term photometric observations of several UX Ori type stars. These stars demonstrate the irregular light variability caused by variable circumstellar extinction. The characteristic time scales of this variability are usually days and weeks. This is superposed on more long lasting and...

Having analyzed long-term series of photometric observations for UX Ori stars (UX Ori, SV Cep, and RZ Psc), we found evidence of possible periodicities in their variability. Multiperiod variability with a nonlinear interaction of periods (modulation) was suspected in SV Cep. The cyclic variability is probably caused by large-scale nonuniformities i...

Based on long-term series of photoelectric observations of the UX Ori stars BF Ori, RR Tau, and CO Ori, we obtained evidence for the cyclicity of their photometric activity on a time scale from several years to ten years or more. Since the photometric variability of this type of star is attributable to variable circumstellar extinction and is deter...

The flares fine structure lies often below the detection limit for photometry data. UBVRI high-speed observations combined with synchronous monitoring at two telescopes situated far from each other allowed us to detect new small-amplitude features in the flare activity of EV Lac. Digital filtering of the light curves with a Gaussian window was used...

During seven years of photopolarimetric monitoring of Herbig Ae star WW Vul 4 deep (Δm > 2 mag) brightness minima were observed. During each of them the degree of linear polarization increased up to 6%. Such a dependence of observed polarization on stellar magnitude agrees well with the now accepted model of variable circumstellar screening. During...

The results of photometric, spectral and radio studies of the flare star EV Lac we obtained during the course of cooperative observations in 1994 and 1995 are presented. A quantitative analysis of the radiation emitted by two powerful flares using the colour-colour diagram confirms the previous conclusion on the essential heterogeneity of matter ra...

The paper presents a new control system for the UBVRI polarimeter constructed at the Helsinki University Observatory and mounted on the 1.25 m telescope of the Crimean Astrophysical Observatory. The optical layout and the operation of the instrument are outlined. The authors justify the need for updating the control system and describe in detail th...

The classical Herbig Ae/Be (HAeBe) star RR Tau is known as a highly variable young star with an amplitude of variability of about 4m in the V pass-band. In this paper we present the results of coordinated Crimea-Dodaira multi-band photo-polarimetric observations of this star which cover fully the observed interval of its brightness changes. Within...

The results of coordinated Crimea-Dodaira simultaneous multi-bands photometric and polarimetric observations of the classical Herbig Ae/Be star RR Tau which cover fully the observed interval of its brightness changes are presented. Within the observed interval of its light variations the linear polarization of RR Tau anti-correlates with its bright...

Results of long-term photometric and polarimetric observations of the classical Herbig Ae star VV Ser, performed at the Crimean Astrophysical Observatory as part of a program of photometric and polarimetric monitoring of UX Ori stars are presented. (1 data file).

The results of the eleven-years (1987-98) photopolarimetric patrol observations of Herbig Ae star SV Cep are presented. Only one deep brightness minimum of star were observed during this time interval. The decrease of the SV Cep brightness during this minimum was accompanied by increase of its linear polarization. The similar behaviour of linear po...