arXiv subjects

Wojtek Pych

Publications and source records attributed to Wojtek Pych.

12 recordsLinked to original sources

arXiv2020

Time Delay of MgII Emission Response for the Luminous Quasar HE 0435-4312: Towards Application of High-Accretor Radius-Luminosity Relation in Cosmology

Using the six years of the spectroscopic monitoring of the luminous quasar HE 0435-4312 ($z=1.2231$) with the Southern African Large Telescope (SALT), in combination with the photometric data (CATALINA, OGLE, SALTICAM, and BMT), we determined the rest-frame time-delay of $296^{+13}_{-14}$ days between the MgII broad-line emission and the ionizing continuum using seven different time-delay inference methods. Artefact time-delay peaks and aliases were mitigated using the bootstrap method, prior weighting probability function as well as by analyzing unevenly sampled mock light curves. The MgII emission is considerably variable with the fractional variability of $\sim 5.4\%$, which is comparable to the continuum variability ($\sim 4.8\%$). Because of its high luminosity ($L_{3000}=10^{46.4}\,{\rm erg\,s^{-1}}$), the source is beneficial for a further reduction of the scatter along the MgII-based radius-luminosity relation and its extended versions, especially when the high-accreting subsample that has an RMS scatter of $\sim 0.2$ dex is considered. This opens up a possibility to use the high-accretor MgII-based radius-luminosity relation for constraining cosmological parameters. With the current sample of 27 reverberation-mapped sources, the best-fit cosmological parameters $(\Omega_{\rm m}, \Omega_{\Lambda})=(0.19; 0.62)$ are consistent with the standard cosmological model within 1$\sigma$ confidence level.

astro-ph.GA↗

arXiv2020

Validating post-AGB candidates in the LMC and SMC using SALT spectra

We selected a sample of post-AGB candidates in the Magellanic Clouds on the basis of their near- and mid-infrared colour characteristics. Fifteen of the most optically bright post-AGB candidates were observed with the South African Large Telescope in order to determine their stellar parameters and thus to validate or discriminate their nature as post-AGB objects in the Magellanic Clouds. The spectral types of absorption-line objects were estimated according to the MK classification, and effective temperatures were obtained by means of stellar atmosphere modelling. Emission-line objects were classified on the basis of the fluxes of the emission lines and the presence of the continuum. Out of 15 observed objects, only 4 appear to be genuine post-AGB stars (27\%). In the SMC, 1 out of 4 is post-AGB, and in the LMC, 3 out 11 are post-AGB objects. Thus, we can conclude that the selected region in the colour-colour diagram, while selecting the genuine post-AGB objects, overlaps severely with other types of objects, in particular young stellar objects and planetary nebulae. Additional classification criteria are required to distinguish between post-AGB stars and other types of objects. In particular, photometry at far-IR wavelengths would greatly assist in distinguishing young stellar objects from evolved ones. On the other hand, we showed that the low-resolution optical spectra appear to be sufficient to determine whether the candidates are post-AGB objects.

astro-ph.SR↗

arXiv2020

Time-delay measurement of MgII broad line response for the highly-accreting quasar HE 0413-4031: Implications for the MgII-based radius-luminosity relation

We present the monitoring of the AGN continuum and MgII broad line emission for the quasar HE 0413-4031 ($z=1.38$) based on the six-year monitoring by the South African Large Telescope (SALT). We managed to estimate a time-delay of $302.6^{+28.7}_{-33.1}$ days in the rest frame of the source using seven different methods: interpolated cross-correlation function (ICCF), discrete correlation function (DCF), $z$-transformed DCF, JAVELIN, two estimators of data regularity (Von Neumann, Bartels), and $\chi^2$ method. This time-delay is below the value expected from the standard radius-luminosity relation. However, based on the monochromatic luminosity of the source and the SED modelling, we interpret this departure as the shortening of the time-delay due to the higher accretion rate of the source, with the inferred Eddington ratio of $\sim 0.4$. The MgII line luminosity of HE 0413-4031 responds to the continuum variability as $L_{\rm line}\propto L_{\rm cont}^{0.43\pm 0.10}$, which is consistent with the light-travel distance of the location of MgII emission at $R_{\rm out} \sim 10^{18}\,{\rm cm}$. Using the data of 10 other quasars, we confirm the radius-luminosity relation for broad MgII line, which was previously determined for broad H$\beta$ line for lower-redshift sources. In addition, we detect a general departure of higher-accreting quasars from this relation in analogy to H$\beta$ sample. After the accretion-rate correction of the light-travel distance, the MgII-based radius-luminosity relation has a small scatter of only $0.10$ dex.

astro-ph.GA↗

arXiv2019

Time delay measurement of Mg II line in CTS C30.10 with SALT

We report 6 yr monitoring of a distant bright quasar CTS C30.10 (z = 0.90052) with the Southern African Large Telescope (SALT). We measured the rest-frame time-lag of $562\pm 2$ days between the continuum variations and the response of the Mg II emission line, using the Javelin approach. More conservative approach, based on five different methods, imply the time delay of $564^{+109}_{-71}$ days. This time delay, combined with other available measurements of Mg II line delay, mostly for lower redshift sources, shows that the Mg II line reverberation implies a radius-luminosity relation very similar to the one based on a more frequently studied H$\beta$ line.

astro-ph.GA↗

arXiv2014

The dust origin of the Broad Line Region and the model consequences for AGN unification scheme

We propose a very simple physical mechanism responsible for the formation of the Low Ionization Line part of the Broad Line Region in Active Galactic Nuclei. It explains the scaling of the Broad Line Region size with the monochromatic luminosity, including the exact slope and the proportionality constant, seen in the reverberation studies of nearby sources. The scaling is independent from the mass and accretion rate of an active nucleus. The mechanism predicts the formation of a dust-driven wind in the disk region where the local effective temperature of a non-illuminated accretion disk drops below 1000 K and allows for dust formation. We explore now the predictive power of the model with the aim to differentiate between this model and the previously proposed mechanisms of the formation of the Broad Line Region. We discuss the expected departures from the universal scaling at long wavelength, and the role of the inclination angle of the accretion disk in the source. We compare the expected line profiles with Mg II line profiles in the quasars observed by us with the SALT telescope. We also discuss the tests based on the presence or absence of the broad emission lines in low luminosity active galaxies. Finally, we discuss the future tests of the model to be done with expected ground-based observations and satellite missions.

astro-ph.GA↗

arXiv2006

Radial Velocity Studies of Close Binary Stars. XI

Radial-velocity measurements and sine-curve fits to the orbital radial velocity variations are presented for ten close binary systems: DU Boo, ET Boo, TX Cnc, V1073 Cyg, HL Dra, AK Her, VW LMi, V566 Oph, TV UMi and AG Vir. By this contribution, the DDO program has reached the point of 100 published radial velocity orbits. The radial velocities have been determined using an improved fitting technique which uses rotational profiles to approximate individual peaks in broadening functions. Three systems, ET Boo, VW LMi and TV UMi, were found to be quadruple while AG Vir appears to be a spectroscopic triple. ET Boo, a member of a close visual binary with $P_{vis} = 113$ years, was previously known to be a multiple system, but we show that the second component is actually a close, non-eclipsing binary. The new observations enabled us to determine the spectroscopic orbits of the companion, non-eclipsing pairs in ET Boo and VW LMi. The particularly interesting case is VW LMi, where the period of the mutual revolution of the two spectroscopic binaries is only 355 days. While most of the studied eclipsing pairs are contact binaries, ET Boo is composed of two double-lined detached binaries and HL Dra is single-lined detached or semi-detached system. Five systems of this group were observed spectroscopically before: TX Cnc, V1073 Cyg, AK Her (as a single-lined binary), V566 Oph, AG Vir, but our new data are of much higher quality than the previous studies.

astro-ph↗

arXiv2005

SN 2005bf: A Possible Transition Event Between Type Ib/c Supernovae and Gamma Ray Bursts

We present u'g'r'i'BV photometry and optical spectroscopy of the Type Ib/Ic SN 2005bf covering the first ~100 days following discovery. The u'g'BV light curves displayed a double-peaked morphology, which is among Type Ib/Ic supernovae. The bolometric light curve indicates that SN 2005bf was a remarkably luminous event. Spectroscopically, SN 2005bf underwent a unique transformation from a Type Ic-like event at early times to a typical Type Ib supernova at later phases. The initial maximum in u'g'BV was accompanied by the presence in the spectrum of high velocity absorption lines of Fe II, Ca II, and H I. The photospheric velocity derived from spectra at early epochs was unusually low compared with ordinary Type Ib supernovae. We describe one-dimensional computer simulations which attempt to account for these remarkable properties. The most favored model is that of a very energetic (2 x 10^{51} erg), asymmetric explosion of a massive (8.3 M_sun) Wolf-Rayet WN star that had lost most of its hydrogen envelope. We speculate that an unobserved relativistic jet was launched producing a two-component explosion consisting of 1) a polar explosion containing a small fraction of the total mass and moving at high velocity, and 2) the explosion of the rest of the star. At first, only the polar explosion is observed, producing the initial maximum and the high velocity absorption-line spectrum resembling a Type Ic event. At late times, this fast-moving component becomes optically-thin, revealing the slower-moving explosion of the rest of the star and transforming the observed spectrum to that of a typical Type Ib supernova. If this scenario is correct, then SN 2005bf is the best example to date of a transition object between normal Type Ib/Ic supernovae and gamma ray bursts.

astro-ph↗

arXiv2005

Radial Velocity Studies of Close Binary Stars.X

Radial-velocity measurements and sine-curve fits to the orbital velocity variations are presented for the ninth set of ten close binary systems: V395 And, HS Aqr, V449 Aur, FP Boo, SW Lac, KS Peg, IW Per, V592 Per, TU UMi, FO Vir. The first three are very close, possibly detached, early-type binaries and all three require further investigation. Particularly interesting is V395 And whose spectral type is as early as B7/8 for a 0.685 day orbit binary. KS Peg and IW Per are single-line binaries, with the former probably hosting a very low mass star. We have detected a low-mass secondary in an important semi-detached system FO Vir at q=0.125+/-0.005. The contact binary FP Boo is also a very small mass-ratio system, q=0.106+/-0.005. The other contact binaries in this group are V592 Per, TU UMi and the well known SW Lac. V592 Per and TU UMi have bright tertiary companions; for these binaries, and for V395 And, we used a novel technique of the broadening functions arranged into a 2-dimensional image in phase. The case of TU UMi turned out intractable even using this approach and we have not been able to derive a firm radial velocity orbit for this binary. Three systems of this group were observed spectroscopically before: HS Aqr, SW Lac, KS Peg.

astro-ph↗

arXiv2003

Radial Velocity Studies of Close Binary Stars. IX

Radial-velocity measurements and sine-curve fits to the orbital velocity variations are presented for the eighth set of ten close binary systems: AB And, V402 Aur, V445 Cep, V2082 Cyg, BX Dra, V918 Her, V502 Oph, V1363 Ori, KP Peg, V335 Peg. Half of the systems (V445 Cep, V2082 Cyg, V918 Her, V1363 Ori, V335 Peg) were discovered photometrically by the Hipparcos mission and all systems are double-lined (SB2) contact binaries. The broadening function method permitted improvement of the orbital elements for AB And and V502 Oph. The other systems have been observed for radial velocity variations for the first time; in this group are five bright (V<7.5) binaries: V445 Cep, V2082 Cyg, V918 Her, KP Peg and V335 Peg. Several of the studied systems are prime candidates for combined light and radial-velocity synthesis solutions.

astro-ph↗

arXiv2003

A Fast Algorithm for Cosmic Rays Removal from Single Images

We present a method for detecting cosmic rays in single images. The algorithm is based on simple analysis of the histogram of the image data and does not use any modeling of the picture of the object. It does not require a good signal to noise ratio in the image data. Identification of multiple-pixel cosmic-ray hits is realized by running the procedure for detection and replacement iteratively. The tests performed by us, show that the method is very effective, when applied to the images with the spectroscopic data. It is also very fast in comparison with other single image algorithms found in astronomical data processing packages. Practical implementation and examples of application are presented.

astro-ph↗

arXiv2001

Cluster AgeS Experiment. CCD photometry of SX Phoenicis variables in the globular cluster M 55

We present CCD photometry of SX Phe variables in the field of the globular cluster M 55. We have discovered 27 variables, three of which are probable members of the Sagittarius dwarf galaxy. All of the SX Phe stars in M 55 lie in the blue straggler region of the cluster color-magnitude diagram. Using period ratio information we have identified the radial pulsation modes for one of the observed variables. Inspection of the period-luminosity distribution permits the probable identifications of the pulsation modes for most of the rest of the stars in the sample. We have determined the slope of the period-luminosity relation for SX Phe stars in M 55 pulsating in the fundamental mode. Using this relation and the HIPPARCOS data for SX Phe itself, we have estimated the apparent distance modulus to M 55 to be (m-M)_V=13.86 +- 0.25 mag.

astro-ph↗

arXiv1999

CCD Photometry of Faint Variable Stars in the Globular Cluster NGC 6752

We present the results of a photometric survey for variable stars in the field of the nearby globular cluster NGC 6752. The cluster was monitored in 1996 and 1997 for a total of 54 hours with 3 different CCD cameras mounted on the 1.0-m Swope telescope. Eleven new variables were identified: 3 SX Phe stars, 7 contact binaries and 1 candidate detached eclipsing binary. All 3 SX Phe variables are likely members of the cluster while only 1 out of the 7 contact binaries is a potential cluster member. As a by-product of our survey we obtained UBV photometry for a large sample of stars in the cluster field. Two stars with U-B \approx -1.0 and V=19.3 and V=20.6 were identified. They lie along the extended horizontal branch of the cluster, and are likely to be faint sdB stars from NGC 6752.

astro-ph↗