arXiv subjects
Publications and source records attributed to N. Petrov.
The new 1.5~m telescope (AZ1500) is operating at the National Astronomical Observatory Rozhen, Bulgaria. This paper gives an overview of the telescope and presents a snapshot of the current performance. Science observations are under way, and we give brief highlights from a number of programs that have been enabled.
We determined shock speed in the Galactic supernova remnant Cygnus Loop, using proper motion of its optical filaments and the latest estimate for its distance. The proper motion was measured by comparing H$α$ images of the remnant observed in two epochs: 1993 (Kitt Peak National Observatory) and 2018/2019 (National Astronomical Observatory Rozhen and Astronomical station Vidojevica). We derived shock speed for 35 locations along different filaments, which is twice as much as in earlier studies of north-eastern part of Cygnus Loop. For the first time, we have measured shock speed of radiative filaments in this region. Three of the analyzed locations where we measured proper motion of filaments are radiative, based on their presence in [SII] images from the second epoch. The other filaments are non-radiative. The speed we obtained for the non-radiative filaments is in the range of 240-650 $\mathrm{km\ s^{-1}}$, with an estimate for the uncertainty of 70 $\mathrm{km\ s^{-1}}$. These values are mostly in agreement with previous studies. The radiative filaments have lower speed of 100-160$\pm${70} $\mathrm{km\ s^{-1}}$, which is in agreement with the assumption that they are older in evolutionary terms. This clear distinction between the speed of the two types of filaments proves that the [SII] emission can be used for identifying radiative filaments in supernova remnants.
We report photometric observations of the hidden symbiotic star SU Lyn in the optical bands. In five nights we detect a weak flickering in U band with amplitude of about 0.05 magnitudes. No intranight variations are found in B, V, g' and r' bands. This is one more indication that the secondary component is a white dwarf accreting at low accretion rate. We also searched for intranight variability of a dozen related object (RR Boo, RT Boo, AM Cyg, AG Peg, BF Cyg, NQ Gem, StHa190, V627 Cas, XX Oph, FS Cet and Y Gem) in which no variability above the observational errors is detected.
In this paper we present new optical observations of the galaxy NGC 185 intended to reveal the status of supernova remnants (SNRs) in this dwarf companion of the Andromeda galaxy. Previously, it was reported that this galaxy hosts one SNR. Our deep photometric study with the 2m telescope at Rozhen National Astronomical Observatory using narrow-band H$α$ and [SII] filters revealed complex structure of the interstellar medium in the center of the galaxy. To confirm the classification and to study the kinematics of the detected nebulae, we carried out spectroscopic observations using the SCORPIO multi-mode spectrograph at the 6m telescope at the Special Astrophysical Observatory of the Russian Academy of Science, both in low- and high-resolution modes. We also searched the archival X-ray and radio data for counterparts of the candidate SNRs identified by our optical observations. Our observations imply the presence of one more SNR, one possible HII region previously cataloged as part of an SNR, and the presence of an additional source of shock ionization in one low-brightness PN. We detected enhanced [SII]/H_alpha and [NII]/H_alpha line ratios, as well as relatively high (up to 90 km s$^{-1}$) expansion velocities of the two observed nebulae, motivating their classification as SNRs (with diameters of 45 pc and 50 pc), confirmed by both photometric and spectral observations. The estimated electron density of emission nebulae is 30 - 200 cm$^{-3}$. Archival XMM-Newton observations indicate the presence of an extended, low-brightness, soft source in projection of one of the optical SNRs, whereas the archival VLA radio image shows weak, unresolved emission in the center of NGC 185.
We present detection of 67 HII regions and two optical supernova remnant (SNR) candidates in the nearby irregular galaxy NGC 2366. The SNR candidates were detected by applying [SII]/H$α$ ratio criterion to observations made with the 2-m RCC telescope at Rozhen National Astronomical Observatory in Bulgaria. In this paper we report coordinates, diameters, H$α$ and [SII] fluxes for detected objects across the two fields of view in NGC 2366 galaxy. Using archival XMM-Newton observations we suggest possible X-ray counterparts of two optical SNR candidates. Also, we discard classification of two previous radio SNR candidates in this galaxy, since they appear to be background galaxies.
Photometric observations in Sloan g' and i' bands of four W UMa stars, NSVS 2244206, NSVS 908513, CSS J004004.7+385531, VSX J062624.4+570907, are presented. The light curve solutions reveal that all targets have overcontact configurations with fillout factor within 0.15-0.26. Their components are of G-K spectral type and almost in thermal contacts. They are relatively close also in size and luminosity: the radius rations r_2/r_1 are within 0.75-0.90; the luminosity ratios l_2/l_1 are within 0.53-0.63. The results of the light curve solution of CSS J004007.7+385531 imply weak limb-darkening effect of its primary component and possible presence of additional absorbing feature in the system.
We present the detection of 16 optical supernova remnant (SNR) candidates in the nearby spiral galaxy IC342. The candidates were detected by applying [SII]/H$α$ ratio criterion on observations made with the 2 m RCC telescope at Rozhen National Astronomical Observatory in Bulgaria. In this paper, we report the coordinates, diameters, H$α$ and [SII] fluxes for 16 SNRs detected in two fields of view in the IC342 galaxy. Also, we estimate that the contamination of total H$α$ flux from SNRs in the observed portion of IC342 is 1.4%. This would represent the fractional error when the star formation rate (SFR) for this galaxy is derived from the total galaxy's H$α$ emission.
We present observations of the portion of the nearby spiral galaxy IC342 using narrow band [SII] and H$α$ filters. These observations were carried out in November 2011 with the 2m RCC telescope at Rozhen National Astronomical Observatory in Bulgaria. In this paper we report coordinates, diameters, H$α$ and [SII] fluxes for 203 HII regions detected in two fields of view in IC342 galaxy. The number of detected HII regions is 5 times higher than previously known in these two parts of the galaxy.
We consider the electromagnetic field in a cavity with a periodically oscillating perfectly reflecting boundary and show that the mathematical theory of circle maps leads to several physical predictions. Notably, well-known results in the theory of circle maps (which we review briefly) imply that there are intervals of parameters where the waves in the cavity get concentrated in wave packets whose energy grows exponentially. Even if these intervals are dense for typical motions of the reflecting boundary, in the complement there is a positive measure set of parameters where the energy remains bounded.