Rozhen National Astronomical Observatory Research Articles

Size of the accretion disc in the recurrent nova T CrB

AbstractWe present high‐resolution (0.06 Å px) spectroscopic observations of the recurrent nova T Coronae Borealis obtained during the last 1.5 years (September 2022–January 2024), with the 2.0‐m RCC telescope of the Rozhen National Astronomical Observatory, Bulgaria. Double‐peaked emission is visible in the line after the end of the superactive state. We subtract the red giant contribution and measure the distance between the peaks () of the line. For the period July 2023–January 2024, we find that is in range km s. Assuming that the emission is from the accretion disc around the white dwarf, we find average radius of the accretion disc R, which is approximately equal to the Roche lobe size of the white dwarf. Our results indicate that tidal torque plays an important role but that the disc can extend up to the Roche lobe of the accreting star.

Results of a long-term optical variability study of 11 quasars and VRI photometry of comparison stars

ABSTRACT We present the results of a 15-yr long-term optical monitoring of 11 quasars conducted with the 2-m Ritchey–Chretien–Coude and the 50/70 cm Schmidt telescopes at the Rozhen National Astronomical Observatory, Bulgaria. Our observations are performed with standard Johnson-Cousins $VRI$ band filters and for each quasar we present a set of comparison standard stars that can be used for monitoring of objects in these fields (including finding charts for the stars identification). The variability and periodicity of each quasar are analysed individually and discussed. The physical properties of each quasar, such as their classification, redshift, and radio structures, are also discussed based on previous literature. Damped random walk model shows the best or the second best fit to the light curves of all objects. However, in six cases periodic models provide comparably good fits and make these six objects a valuable addition to the growing sample of quasars with periodic flux variation. They will be suitable for further investigation of the hitherto unclear mechanisms that give rise to this variability pattern. Our results provide important insights into the long-term variability and physical properties of quasars, which can further deepen our understanding of the nature and evolution of active galaxy nuclei.

Polarimetric Reverberation Mapping in Medium-Band Filters

Earlier, we suggested the “reload” concept of the polarimetric reverberation mapping of active galactic nuclei (AGN), proposed for the first time more than 10 years ago. We have successfully tested this approach of reverberation mapping of the broad emission line on the galaxy Mrk 6. It was shown that such an idea allows one to look at the AGN central parsec structure literally in a new light. However, the method originally assumed the use of spectropolarimetric observations, expensive in terms of telescope time, and implemented on rare large telescopes. Currently, we propose an adaptation of the polarimetric reverberation mapping of broad lines in medium-band filters following the idea of the photometric reverberation mapping, when filters are selected so that their bandwidth is oriented to the broad line and the surrounding continuum near. In this paper, we present the progress status of such monitoring conducted jointly at the Special astrophysical observatory and Asiago Cima Ekar observatory (OAPd/INAF) with support from Rozhen National Astronomical Observatory (NAO), some first results for the most frequently observed AGNs Mrk 335, Mrk 509, and Mrk 817, and the discussion of the future perspectives of the campaign.

Proper motion of Cygnus Loop shock filaments

We determined the shock speed in the Galactic supernova remnant Cygnus Loop, using the proper motion of its optical filaments and the latest estimate of its distance. The proper motion was measured by comparing H? 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 the north-eastern part of the Cygnus Loop. For the first time, we have measured the shock speed of the radiative filaments in this region. Three of the analyzed locations where we measured the 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 km s-1, with an estimate for the uncertainty of 70 km s-1. These values are mostly in agreement with previous studies. The radiative filaments have lower speeds of 100-160 ?70 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 [SII] emission can be used for identifying radiative filaments in supernova remnants.

Interstellar polarization and extinction toward the Recurrent Nova T CrB

Spectropolarimetry is a powerful tool for diagnostic of interstellar matter and gives information about the geometry of the ejected material after the novae outbursts. In this paper are presented spectropolarimetric observations of the recurrent nova T CrB at quiescence obtained with FoReRo2 attached to the Cassegrain focus of the 2.0 m RCC telescope of the Bulgarian Rozhen National Astronomical Observatory. The interstellar polarization toward T CrB was estimated using the field stars method. The spectropolarimetric observations were obtained from February 2018 to August 2021. In the wavelength range from 4800 Å to 8200 Å the maximum of the degree of linear polarization is Pmax(obs)(%)=0.46±0.01 at λ≈5200 Å. The position angle is P.A.obs=100°.8±0°.9. During the observations, there is no intrinsic polarization in T CrB, and the derived values represent interstellar polarization. The polarization toward T CrB is due to the foreground interstellar dust located at the distance up to ≈ 400 pc. Based on the degree of polarization the interstellar extinction toward T CrB is EB−V≈0.07.

Second Version of SpectraView for Spectra Analysis

Abstract This short communication presents a second version of the program SpectraView (SV2). The Second Version of SpectraView for Spectra Analysis is based on data collected with 2-m RCC telescope at Rozhen National Astronomical Observatory. This version is equipped with new user interface and other features unavailable in its previous versions. It has also been created using modern programming language and is now compatible with the latest operating systems. The program has been tested on the observations of the five short-period variable stars.

Revealing the nature of central emission nebulae in the dwarf galaxy NGC 185

Aims. 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. Methods. Our deep photometric study with the 2m telescope at Rozhen National Astronomical Observatory using narrow-band Hα and [S II] 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. Results. Our observations imply the presence of one more SNR, one possible H II region previously cataloged as part of an SNR, and the presence of an additional source of shock ionization in one low-brightness planetary nebula. We detected enhanced [S II]/Hα and [N II]/Hα 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.

Optical observations of the nearby galaxy NGC 2366 through narrowband Hα and [SII] filters. Supernova remnants status

We present detection of 64 H II regions, three superbubbles and two optical supernova remnant (SNR) candidates in the nearby irregular galaxy NGC 2366. The SNR candidates were detected by applying [S II]/H? 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? and [S II] fluxes for detected objects across the two fields of view in the 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.

Long-term BV RI photometric light curves of 15 PMS stars in the star-forming region IC 5070**Based on observations obtained at the Rozhen National Astronomical Observatory, Bulgaria. The photometric data are only available at CDS.

This paper reports results from the multicolor photometric observations of 15 pre-main sequence stars collected in the period September 2010 – October 2017. The stars from our study are located in the star-forming HII region IC 5070. These objects were previously detected as either emission line stars, flare stars, T Tauri variables or Herbig Ae/Be stars. Photometric observations, especially concerning the long-term behavior of the objects, are missing in the literature. We present the first photometric monitoring for all stars from our study. The analysis of the obtained BV RI photometric data allows us to draw the conclusion that all investigated objects are variable stars. In the case of LkHα 146, we identified previously unknown periodicity in its photometric variability.

Preliminary Results of Low Dispersion Asteroid Spectroscopy Survey at NAO Rozhen

AbstractWe are presenting the first results of low dispersion spectroscopic observation of asteroids at Bulgarian National Astronomical Observatory Rozhen. Asteroids with unclassified spectra and brighter than 15 magnitude have been chosen. Besides just presenting the asteroid reflectance, classification according to Bus S. J. et al. (2012) has been done. The asteroid spectra of 590 Tomyris, 703 Noemi, 1596 Itzigsohn and 1826 Miller are presented together with standard spectra corresponding to the three best matches given by the public software tool M4AST (Popescu M. et al. (2012)). Our aim is to participate in the coordinated program of asteroids spectroscopy complementary to the observations of Gaia.

Long-term photometric behavior of the PMS stars V977 Cep and V982 Cep in the vicinity of NGC 7129**Based on observations obtained at Rozhen National Astronomical Observatory, Bulgaria.

Long-term BV RI photometric light curves of the pre-main sequence stars V977 Cep and V982 Cep during the period from 2000 October to 2016 August are presented. The stars are located in the vicinity of the reflection nebula NGC 7129. Our photometric data show that both stars exhibit strong photometric variability in all optical passbands, which is typical for Classical T Tauri stars. Using our observational data we analyze the reasons for the observed brightness variations. In the case of V977 Cep we identify previously unknown periodicity in its light curve.

Imaging polarimetry and spectropolarimetry of comet C/2013 R1 (Lovejoy)

We have obtained imaging polarimetry of the comet C/2013 R1 (Lovejoy) with 2-Channel-Focal-Reducer Rozhen instrument at 2m Ritchey–Chrétien–Coudé telescope of the Bulgarian National Astronomical Observatory Rozhen in two dust continuum filters covering wavelength intervals clear from molecular emissions and centred at 4430Å in blue filter and at 6840Å in red filter. In imaging mode we measured the degree of linear polarisation 17.01±0.09% in the blue and 18.81±0.02% in the red, which is in a very good agreement with measurements of other comets at the similar phase angle. We have also obtained polarisation maps in both filters. We found a strong correlation between the spatial distribution of the polarisation and the dust colour. Spectropolarimetry of the nucleus region shows an increase of the polarisation with wavelength, and a depolarisation in the spectral regions with gas emission lines, most noticeable in C2 emission band, which shows a polarisation of 6.0±1.1%.

Orbital parameters of the high‐mass X‐ray binary 4U 2206+54

AbstractWe present new radial velocities of the high‐mass X‐ray binary star 4U 2206+54 based on optical spectra obtained with the Coudé spectrograph at the 2 m RCC telescope of the Rozhen National Astronomical Observatory, Bulgaria in the period November 2011–July 2013. The radial velocity curve of the He I δ6678 Å line is modeled with an orbital period Porb = 9.568 d and an eccentricity of e = 0.3. These new measurements of the radial velocity resolve the disagreements of the orbital period discussions. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photometry and shape modeling of Mars crosser asteroid (1011) Laodamia

An analysis of photometric observations of Mars crosser asteroid 1011 Laodamia conducted at Bulgarian National Astronomical Observatory Rozhen over a twelve year interval (2002, 2003, 2004, 2006, 2007, 2008, 2011, 2012 and 2013) is made. Based on the obtained lightcurves the spin vector, sense of rotation, and preliminary shape model of (1011) Laodamia have been determined using the lightcurve inversion method. The aim of this investigation is to increase the set of asteroids with known spin and shape parameters and to contribute in improving the model in combination with other techniques and sparse data produced by photometric asteroid surveys such as Pan-STARRS or GAIA.

Optical observations of the nearby galaxy IC342 with narrow band [SII] and Hα filters. I

We present observations of a portion of the nearby spiral galaxy IC342 using narrow band [SII] and H? 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? 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.

The Wide-Field Plate Database: Development and Access via Internet

The motivations and results from the first 1.5-year period of the project “Wide-field Plate Database (WFPDB): Development and Access via Internet” (DO-02-273/18.12.2008), approved for funding through a competition held by the Bulgarian National Science Fund in the field of Promotion of Research in Priority Areas, are described. The main direction of the development of the project is digitization and preservation of, and web access to, the astronomical plate archives of the 2-m RCC and the 50/70 cm Schmidt telescopes of the Rozhen National Astronomical Observatory received in the period 1979–1998. The basis of the work is set out in Tsvetkov (2006) [1] and Tsvetkova & Tsvetkov (2006) [2], motivating the project over the past 10 years. The WFPDB (www.wfpdb.org) represents a unique virtual instrument in astronomical research, which allows obtaining information on existing astronomical observations of celestial objects over the past 130 years with the professional astronomical telescopes at observatories around the world. Briefly, this is a unique virtual telescope working as a “Time Machine” for obtaining information on historical observations of minor planets, comets, stars and galaxies. The project also aims to continue and expand the successful work initiated during the past 15 years by extending the provision of technical work on the base, and improving and extending the internal LAN (www.skyarchive.org), which ensures rapid online access to data, based on international standards of the International Virtual Observatory Alliance (IVOA) and the European Virtual Observatory (EURO-VO). The main results of this paper are described in detail in the annual report project of July 15, 2010: http://trillian.magrathea.bg:8181/DATABASE FNI 273 2010July/

Rotation-stimulated structures in the CN and C3comae of comet 103P/Hartley 2 close to the EPOXI encounter

In late 2010 a Jupiter Family comet 103P/Hartley 2 was a subject of an intensive world-wide investigation. On UT October 20.7 the comet approached the Earth within only 0.12 AU, and on UT November 4.6 it was visited by NASA's EPOXI spacecraft. We joined this international effort and organized an observing campaign. The images of the comet were obtained through narrowband filters using the 2-m telescope of the Rozhen National Astronomical Observatory. They were taken during 4 nights around the moment of the EPOXI encounter. Image processing methods and periodicity analysis techniques were used to reveal transient coma structures and investigate their repeatability and kinematics. We observe shells, arc-, jet- and spiral-like patterns, very similar for the CN and C3 comae. The CN features expanded outwards with the sky-plane projected velocities between 0.1 to 0.3 km/s. A corkscrew structure, observed on November 6, evolved with a much higher velocity of 0.66 km/s. Photometry of the inner coma of CN shows variability with a period of 18.32+/-0.30 h (valid for the middle moment of our run, UT 2010 Nov. 5.0835), which we attribute to the nucleus rotation. This result is fully consistent with independent determinations around the same time by other teams. The pattern of repeatability is, however, not perfect, which is understendable given the suggested excitation of the rotation state, and the variability detected in CN correlates well with the cyclic changes in HCN, but only in the active phases. The revealed coma structures, along with the snapshot of the nucleus orientation obtained by EPOXI, let us estimate the spin axis orientation. We obtained RA=122 deg, Dec=+16 deg (epoch J2000.0), neglecting at this point the rotational excitation.

BVRIphotometry of NGC 3231, NGC 7055, and NGC 7127

1 Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlarska 2, 611 37 Brno, Czech Republic e-mail: epaunzen@physics.muni.cz 2 Rozhen National Astronomical Observatory, Institute of Astronomy of the Bulgarian Academy of Sciences, PO Box 136, 4700 Smolyan, Bulgaria 3 Sandvretens Observatory, Linnegatan 5A, 75332 Uppsala, Sweden Received 16 November 2011 / Accepted 22 April 2012

Recent Spectral Observations of Epsilon Aurigae in the Near-IR

AbstractHigh resolution spectral observations of ϵ Aur were carried out in the near-IR spectral range. Observations were obtained with the Coudé-spectrograph of the 2m RCC telescope at National Astronomical Observatory Rozhen and cover all main phases of the current eclipse. Results revealed for the first time absorption components in O I and Ca II triplets and variations of N I lines. Estimation of the electron density was done using lines from the Paschen series of hydrogen.

Characterizing New Eclipsing Binaries Identified from STEREO Photometry

AbstractSince 2010, a program to explore new eclipsing binary systems identified from STEREO photometry has been in progress. Our first results are presented here: light curves and high resolution spectra taken with Coudé spectrograph (National Astronomical Observatory Rozhen) and ARC Échelle spectrometer (ARCES, Apache Point Observatory).