D. Dimitrov
A5074038002- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- Adaptive optics and wavefront sensing
- Solar and Space Plasma Dynamics
- Calibration and Measurement Techniques
- Atmospheric Ozone and Climate
- Geophysics and Gravity Measurements
- Pulsars and Gravitational Waves Research
- Material Science and Thermodynamics
- Galaxies: Formation, Evolution, Phenomena
- Image Processing Techniques and Applications
- Radio Astronomy Observations and Technology
- Optical Systems and Laser Technology
- Nuclear Physics and Applications
- Historical Astronomy and Related Studies
- Dark Matter and Cosmic Phenomena
- Game Theory and Voting Systems
- Geophysics and Sensor Technology
- Infrared Target Detection Methodologies
Saarland University
2024
Institute of Astronomy and National Astronomical Observatory
2013-2022
Shumen University
2017-2018
Bulgarian Academy of Sciences
2007-2015
Institute of Astronomy
2005
ABSTRACT OJ 287 is a quasi-periodic quasar with roughly 12 year optical cycles. It displays prominent outbursts that are predictable in binary black hole model. The model predicted major outburst 2015 December. We found the did occur within expected time range, peaking on December 5 at magnitude 12.9 R -band. Based Swift /XRT satellite measurements and polarization data, we find it included thermal component. Its timing provides an accurate estimate for spin of primary hole, . present also...
The transiting planet WASP-12 b was identified as a potential target for transit timing studies because departure from linear ephemeris reported in the literature. Such deviations could be caused by an additional system. We attempt to confirm existence of claimed variations and interpret its origin. organised multi-site campaign observe transits three observing seasons, using 0.5-2.6-metre telescopes. obtained 61 light curves, many them with sub-millimagnitude precision. simultaneous...
Abstract We present the results of our power spectral density analysis for BL Lac object OJ 287, utilizing Fermi -LAT survey at high-energy γ -rays, Swift -XRT in X-rays, several ground-based telescopes and Kepler satellite optical, radio GHz frequencies. The light curves are modeled terms continuous-time autoregressive moving average (CARMA) processes. Owing to inclusion data, we were able construct first time optical variability spectrum a blazar without any gaps across ∼6 dex temporal Our...
Photometric follow-ups of transiting exoplanets may lead to discoveries additional, less massive bodies in extrasolar systems. This is possible by detecting and then analysing variations transit timing exoplanets. We present photometric observations gathered 2009 2010 for exoplanet WASP-3b during the dedicated transit-timing-variation campaign. The observed cannot be explained a constant period but periodic variation minus calculations diagram. Simplified models assuming existence perturbing...
We present a new observational campaign, DWARF, aimed at detection of circumbinary extrasolar planets using the timing minima low-mass eclipsing binaries. The observations will be performed within an extensive network relatively small to medium-size telescopes with apertures ~20-200 cm. starting sample objects monitored contains (i) binaries M and K components, (ii) short-period sdB or sdO component, (iii) post-common-envelope systems containing WD, which enable determine high precision....
We study the mid-egress eclipse timing data gathered for cataclysmic binary HU Aquarii during years 1993–2014. The (O−C) residuals were previously attributed to a single ∼7 Jupiter mass companion in ∼5 au orbit or stable two-planet system with an unconstrained outermost orbit. present 22 new observations between 2011 June and 2014 July four instruments around world. They reveal systematic deviation of ∼60–120 s from older ephemeris. re-analyse whole set available. Our results provide erratum...
Aims. Most hot Jupiters are expected to spiral in toward their host stars because the angular momentum of orbital motion is transferred stellar spin. Their orbits can also precess as a result planet-star interactions. Calculations show that both effects might be detected for very-hot exoplanet WASP-12 b using method precise transit-timing over time span about 10 yr.
We thank the referee for valuable comments which improved paper. also Dr. Laetitia Delrez and Pedro Sada sharing WASP-103 HAT-P-23 light curves with us. GM MS acknowledge financial support from National Science Centre, Poland through grant no. 2016/23/B/ST9/00579. MF acknowledges grants AYA2014-54348-C3-1-R AYA2016-79425-C3-3-P of Spanish Ministry Economy Competitiveness (MINECO), co-funded EU FEDER funds. DD projects DN 08-1/2016, 08-20/2016 Foundation Bulgarian education science as well by...
Transit timing analysis may be an effective method of discovering additional bodies in extrasolar systems which harbour transiting exoplanets. The deviations from the Keplerian motion, caused by mutual gravitational interactions between planets, are expected to generate transit variations In 2009 we collected 9 light curves 8 transits exoplanet WASP-10b. Combining these data with published ones, found that cannot explained a constant period but periodic variation. Simplified three-body...
There have been previous hints that the transiting planet WASP-3 b is accompanied by a second in nearby orbit, based on small deviations from strict periodicity of observed transits. Here we present 17 precise radial velocity measurements and 32 transit light curves were acquired between 2009 2011. These data used to refine parameters host star planet. This has resulted reduced uncertainties for radii masses The radial-velocity times show no evidence an additional system. Therefore,...
We present the Young Exoplanet Transit Initiative (YETI), in which we use several 0.2 to 2.6m telescopes around world monitor continuously young (< 100 Myr), nearby 1 kpc) stellar clusters mainly detect transiting planets (and study other variability phenomena on time-scales from minutes years). The telescope network enables us observe targets for days order not miss any transit. runs are typically one two weeks long, about three per year cluster or subsequent years ten clusters. There...
We present the results of 45 transit observations obtained for transiting exoplanet HAT-P-32b. The transits have been observed using several telescopes mainly throughout YETI network. In 25 cases, complete light curves with a timing precision better than $1.4\:$min obtained. These used to refine system properties, namely inclination $i$, planet-to-star radius ratio $R_\textrm{p}/R_\textrm{s}$, and between semimajor axis stellar $a/R_\textrm{s}$. First analyses by Hartman et al. (2011)...
We carried out photometric and low-resolution spectral observations of six eclipsing ultrashort-period binaries with MS components. The light curve solutions the Rozhen show that all targets are overcontact systems. found well-defined empirical relation "period -- semi-major axis" for short-period used it estimation global parameters targets. Our results revealed NSVS 925605 is quite interesting target: (a) one a few contact M components; (b) exhibits high activity (emission in H$\alpha$...
As part of our ongoing effort to investigate transit timing variations (TTVs) known exoplanets, we monitored transits the four exoplanets HAT-P-18b, HAT-P-19b, HAT-P-27b/WASP-40b and WASP-21b. All them are suspected show TTVs due properties their host systems based on respective discovery papers. During past three years 46 observations were carried out, mostly using telescopes Young Exoplanet Transit Initiative. The analyses used refine systems' orbital parameters. In all cases found no...
In this paper, we present high- and middle-resolution spectral observations of seven heartbeat (HB), highly eccentric, Kepler binaries: four them (KIC 3230227, KIC 03547874, 03749404, 07672068) are SB2 stars the remaining three 04949194, 05960989, 10092506) SB1 stars. The flux amplitudes their HB signals from 0.001 to 0.01. Five targets sample with eccentricity above 0.64 show tidally induced oscillations, which harmonics orbital period. global parameters all were determined as a result...
CCD photometric observations in V RI colors and spectroscopic of the newly discovered eclipsing binary GSC 2314-0530 (NSVS 6550671) with dMe components very short period P = 0.192636 days are presented.The simultaneous light-curve solution radial velocity allows to determine global parameters 2314-0530:The chromospheric activity its is revealed by strong emission Hα line (with mean EW 5 Å) observed several flares.Empirical relations mass-M bol , mass-radius mass-temperature derived on basis...
CVSO 30 is a unique young low-mass system, because, for the first time, close-in transiting and wide directly imaged planet candidates are found around common host star. The inner companion, b, possible orbiting previously known weak-lined T Tauri With five telescopes of 'Young Exoplanet Transit Initiative' located in Asia, Europe South America, we monitored over three years total 144 nights detected 33 fading events. In two more seasons carried out follow-up observations with telescopes. We...
Aims. The transiting hot-Jupiter planet Qatar-1 b exhibits variations in transit times that could be perturbative. A hot Jupiter with a planetary companion on nearby orbit would constitute an unprecedented configuration, which is important for theories of the formation and evolution systems. We performed photometric follow-up campaign to confirm or refute timing variations.
We present new transit light curves for planets in six extrasolar planetary systems. They were acquired with 0.4-2.2 m telescopes located west Asia, Europe, and South America. When combined literature data, they allowed us to redetermine system parameters a homogeneous way. Our results individual systems are agreement values reported previous studies. refined ephemerides reduced uncertainties of orbital periods by factor between 2 7. No sign any variations times was detected the studied.
Abstract We report our investigation of the first transiting planet candidate from YETI project in young (∼4 Myr old) open cluster Trumpler 37. The transit‐like signal detected lightcurve F8V star 2M21385603+5711345 repeats every 1.364894 + 0.000015 days, and has a depth 54.5 0.8 mmag R . Membership is supported by its mean radial velocity location color‐magnitude diagram, while Li diagnostic proper motion are inconclusive this regard. Follow‐up photometric monitoring adaptive optics imaging...
We present new results from optical photometric and spectroscopic observations of the eruptive pre-main sequence star V2493 Cyg (HBC 722). The object has continued to undergo significant brightness variations over past few months is an ideal target for follow-up observations. carried out CCD BVRI in field ("Gulf Mexico") August 1994 April 2012, i.e. at pre-outburst states during phases outburst. acquired high, medium, low resolution spectroscopy To study variability construct its historical...
We present thirteen new transit light curves for the WASP-1 b exoplanet. Observations were acquired with 0.5 - 1.2-m telescopes between 2007 and 2013. Our homogeneous analysis, which also includes literature data, results in determining precise system parameters. New values are agreement those reported previous studies. Transit times follow a linear ephemeris no sign of any time variations. This finding is line paradigm that Jupiter-like planets on tight orbits devoid close planetary companions.
New photoelectric BV light curves of three close eclipsing binaries XY Leo, EE Cet and AQ Psc were observed studied with the aim to derive physical parameters these systems. The following results obtained: (a) W-type contact binary system Leo is in a marginal overcontact configuration (fover ∼ 2.4%) relatively large temperature difference between components (∼330K); (b) due proximity companion visual ADS 2163, contaminated by third light, having impact on system-parameter estimates,...
Aims.The rapidly rotating active stars FK Com and HD 199178 are investigated using extensive long-term photometry. The data set includes previously unpublished photometry, obtained at the Rozhen National Astronomical Observatory. We look for periodicities in photometric behaviour of both stars, as well spots, light curve modelling. Special attention is paid to "flip-flop" phenomenon.
Two observational campaigns were carried out during the eclipses of EE Cep in 2003 and 2008/9 to verify whether eclipsing body system is indeed a dark disk understand observed changes depth durations eclipses. Multicolour photometric data spectroscopic observations at both low high resolution collected. We numerically modelled variations brightness colour tested models with different structure. considered possibility precession. The complete set collected last three are made available...