Optical observations of an infrared selected sample of galaxies

Extragalactic IRAS sources with previously unknown optical counterparts were selected from thePoint Source Catalog within two 300 deg² areas. Deep CCD images have been obtained for 99 objects and long-slit spectroscopy has been performed in 55 fields. The morphological, spectroscopic and photometric properties of these objects are summarized.     

Viewing angles in some selected BL Lac objects

A selected subset of BL Lac objects were monitored with VLBI techniques at multifrequencies. Apparent superluminal motion and X-rays were detected in all of the monitored sources. From the observational data, kinematic parameters, geometric parameters and beaming effects for the core of the selected BL Lac objects have been estimated. Our results indicate that some BL Lacs have large Lorentz factors and small viewing angles; relativistic beaming effects are strongly present in these sources. On the other hand, some BL Lacs have small Lorentz factors; their viewing angles are quite large. It does not seem possible to avoid the fact that some BL Lac objects are not oriented particularly close to the line of sight. It conflicts with the basic assumption of the accepted theories for explaining the characteristics of BL Lac objects at present. Also, it seems that the BL Lac objects in the class I of the Burdige and Hewitt's classification have larger viewing angles than those int he class II. The whole BL Lac classification could be a misnomer: the sources classified as BL Lac objects are a mixture of physically different populations with different parent objects.     

Optical microvariability of selected PG QSOs

This is a preliminary report of the continuing search for significant optical microvariability in a selected sample of radio-quiet and radio-loud quasi-stellar objects (QSOs). Total of 24 Paloma-Green (PG) quasars are observed. Among them, 17 objects are classified as radio-quiet and seven objects are classified radio-loud. In this classification, the ratio R, radio to optical flux density, is required to be less than 1 in order to assure the objects are reasonably radio-quiet. Two out of 17 radio-quiet QSOs and six out of eight radio-loud QSOs were microvariable. This apparent contrast in microvariations between radio-quiet and radio-loud QSOs does not provide firm support for the theoretical model utilizing discrete events in accretion disks and implies substantial support for models based on propagating shocks on relativistic jets as the likely process responsible for producing most of the microvariations are observed in AGNs.     

Determination of the red shifts of selected IVS program objects. I

The spectroscopic red shifts of seven optical objects whose coordinates coincide with those of radio sources in the IVS (International VLBI Service for Geodesy and Astrometry) program list are determined from observations with the 6-m BTA telescope at the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences. A comparison of these spectra and red shifts with data in the radio frequency range shows that four of the objects discussed here are correctly identified, while the other three require further study. The distances to the radio sources derived from our measurements yield more accurate estimates of the cosmological model parameters than those based on the proper motions of these objects derived from geodesic VLBI observations.     

GRB‐selected galaxies

We describe the current status and recent results from our Swift/VLT legacy survey, a VLT Large Programme aimed at characterizing the host galaxies of a homogeneously selected sub‐sample of Swift gamma‐ray bursts (GRBs). The immediate goals are to determine the host luminosity function, study the effects of reddening, determine the fraction of Lyα emitters in the hosts, and obtain redshifts for targets without a reported one. We have defined a very carefully selected sample, obeying strict and well‐defined criteria: 68 targets in total. Among the preliminary results is a large optical detection rate, the lack of extremely red objects (only one possible case in the sample), and 10 new GRB redshifts with the mean redshift of the host sample assessed to be 〈z 〉 ≳ 2 (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the difference between the X-ray selected and the radio selected BL Lac objects in the near infrared

By using results from the 2MASS observation, the differences between the X-ray selected BL Lac objects (XBLs) and the radio selected ones (RBLs) in the near infrared are discussed in this paper. It is found that, statistically, the RBLs have redder near infrared colors and steeper spectral indices in the near infrared than XBLs, whereas the XBLs have more influences from their host galaxies than the RBLs. It is also seen that the RBLs have much brighter luminosity in the near infrared than the XBLs. In addition, the high polarization characteristics are found in common for RBLs, but not for XBLs.     

The radio properties of a sample of optically selected radio-loud quasars

We searched for identification between the Large Bright Quasar Survey and the latest whole-sky survey catalog of 4.85 GHz radio sources. We found 34 quasars to have radio counterparts and they proved to be radio-loud objects. We found a nearly linear correlation between their radio and optical luminosities in this, probably the largest so far, sample of radio-loud quasars.     

Outbursts of selected dwarf novas and postnovas

Observations are presented of selected cataclysmic variables (the dwarf novas V1504 Cyg and GO Com and the postnovas Q Cyg, V446 Her, and DI Lac) carried out at the Crimean Astrophysical Observatory and the Crimean Laboratory of the Sternberg Astronomical Institute in 1995–2007. The outburst parameters and the behavior of these objects on the “magnitude (V)-color (V-R)” diagram are described. The tracks of postnova outbursts on this diagram are similar to the dwarf-nova behavior. On average, all the studied systems show a break on the “brightness-color” dependence. The color V-R before the break increases more weakly than after it or does not increase at all.     

Clustering of X-ray selected active galactic nuclei

A total of 235 active galactic nuclei (AGN) from two different soft X-ray surveys [the ROSAT Deep Survey (DRS) and the ROSAT International X-ray Optical Survey (RIXOS)] with redshifts between 0 and 3.5 are used to study the clustering of X-ray selected AGN and its evolution. A 2σ significant detection of clustering of such objects is found on scales < 40–80 h ⁻¹ Mpc in the RIXOS sample, while no clustering is detected on any scales in the DRS sample. Assuming a single power-law model for the spatial correlation function (SCF), quantitative limits on the AGN clustering have been obtained: a comoving correlation length 1.5 ≲  r ₀ ≲ 3.3  h ⁻¹ Mpc is implied for comoving evolution, while 1.9 ≲  r ₀ ≲ 4.8 for stable clustering and 2.2 ≲  r ₀ ≲ 5.5 for linear evolution. These values are consistent with the correlation lengths and evolutions obtained for galaxy samples, but imply smaller amplitude or faster evolution than recent ultraviolet and optically selected AGN samples. We also constrain the ratio of bias parameters between X-ray selected AGN and IRAS galaxies to be ≲ 1.7 on scales ≲ 10  h ⁻¹ Mpc, a somewhat smaller value than is inferred from local large-scale dynamical studies.     

Observational evidences of multiple shock waves in X-ray selected BL Lacerate objects

The results of optical R-band photometry of three X-ray selected BL Lacertae objects 1ES 0502+675, 1ES 0806+524 and 1ES 1959+650 from the Einstein Slew Survey are presented. The observations are performed during 1997–2006 with the 70-cm meniscus type telescope of Abastumani Astrophysical Observatory. The objects show clear long-term variability with time scales of 1–3 years without evident periodicity. The main results consist in the discovery of multiple-peak structures on historical light curves as predicted theoretically on the basis of the assumption that long-term variability of blazars are triggered by ultrarelativistic shock waves propagating through their jets. They are direct evidence of the existence of reverse shocks besides the main one arising by a single disturbance. Two-peak maxima are found for 1ES 0502+675 and 1ES 0806+524. The more complicated structure shows 1ES 199+650 - a maximum with four consequent peaks. The relative strengths of the main and reverse shocks are mainly equal according to the shape of the respective peaks. The brightness dip between them is on average 60% less than in the case of consequent main shocks. Optical maximum epochs, covered well by the observations, show that the main shocks are either not always accompanied by reverse ones or the later are not always strong enough to be discovered by the observations.     

Evidence of rapid optical variability in selected narrow-line Seyfert 1 galaxies

We present the first results of a search for the presence of rapid optical variability in a sample of five Narrow-Line Seyfert 1 galaxies. We find clear evidence of rapid variability for IRAS 13224-3809 with variations occurring on time scales of an hour. However, the results are less conclusive for the other four sources in our sample, Markarian 766, PG 1244+026, PG 1404+226 and Arakelian 564. While there are several instances among these latter objects where there is a hint that variability may be present, IRAS 13224-3809 provides the only conclusive evidence of rapid optical variability detected to date.     

Spectrum variability of some selected bright CP stars on the main sequence

The initial findings of a survey for spectrum variations in selected CP stars is reported. It is found that almost all observed mercury-manganese stars are spectrum variables. The implications of chemical anomalies in these stars is briefly discussed. In particular, arguments are advanced against the general assumption that CP3 stars are non-magnetic. The observed low rotational velocities of the CP3 stars is interpreted as rotational braking by magnetic fields mostly in the pre-Main-Sequence stage of evolution of these objects. We advance the hypothesis that high resolution spectroscopic observations of such stars would exhibit Zeeman-broadening in lines that vary in strength and are also sensitive to the magnetic field.     

XMM–Newton observations of bright ROSAT selected active galactic nuclei with low intrinsic absorption

We present a sample of 21 ROSAT bright active galactic nuclei (AGNs), representing a range of spectral classes, and selected for follow-up snapshot observations with XMM–Newton . The typical exposure was between 5 and 10 ks. The objects were primarily selected on the bases of X-ray brightness and not on hardness ratio; thus the sample cannot be strictly defined as a 'soft'sample. One of the main outcomes from the XMM–Newton observations was that all of the AGN, including 11 type 1.8–2 objects, required low levels of intrinsic absorption  ( N _H≲ 10²¹ cm⁻²)  . The low absorption in type 2 systems is a challenge to account for in the standard orientation-based unification model, and we discuss possible physical and geometrical models which could elucidate the problem. Moreover, there does not appear to be any relation between the strength and shape of the soft excess, and the spectral classification of the AGN in this sample. We further identify a number of AGN which deserve deeper observations or further analysis: for example, the low-ionization nuclear emission regions (LINERs) NGC 5005 and NGC 7331, where optically thin thermal and extended emission is detected, and the narrow-line Seyfert 1 II Zw 177, which shows a broad emission feature at ∼ 5.8 keV.     

A new reduction of digitized photographic plates with selected asteroids obtained with the normal astrograph of the Pulkovo Observatory from 1948 to 1990

The results of a new reduction of 1545 photographic observations of 14 selected asteroids obtained with the Normal Astrograph of the Pulkovo Observatory from 1948 to 1990 are presented. Photographic plates stored in the archive of the observatory were digitized with a general purpose flatbed scanner using a specially developed technique. The accuracy of the reduction of photographic plates is measured. The UCAC3 catalogue has been used as a reference. Residual differences between coordinates of stars in the reference catalogue are used to analyze and tacking into account obtained instrumental systematic errors. Equatorial coordinates of 1378 individual observations of target asteroids are obtained. They are compared with the results of the reduction of the material made earlier. Among the objects of the background, positions of 1475 stars with large proper motions from the LSPM catalogue are measured.     

Optical spectroscopy of two overlapping, flux-density-limited samples of radio sources in the North Ecliptic Cap, selected at 38 and 151 MHz

We present the results of optical spectroscopy of two flux-density-limited samples of radio sources selected at frequencies of 38 and 151 MHz in the same region around the North Ecliptic Cap, the 8C-NEC and 7C- iii samples respectively. Both samples are selected at flux density levels ≈20 times fainter than samples based on the 3C catalogue. They are amongst the first low-frequency selected samples with no spectral or angular size selection for which almost complete redshift information has been obtained, and contain many of the lowest-luminosity z >2 radio galaxies so far discovered. They will therefore provide a valuable resource for understanding the cosmic evolution of radio sources and their hosts and environments. The 151-MHz 7C- iii sample is selected to have S ₁₅₁≥0.5 Jy and is the more spectroscopically complete; out of 54 radio sources fairly reliable redshifts have been obtained for 44 objects. The 8C sample has a flux limit of S ₃₈≥1.3 Jy and contains 58 sources of which 46 have fairly reliable redshifts. We discuss possible biases in the observed redshift distribution, and some interesting individual objects, including a number of cases of probable gravitational lensing. Using the 8C-NEC and 7C- iii samples in conjunction, we form the first sample selected on low-frequency flux in the rest-frame of the source, rather than the usual selection on flux density in the observed frame. This allows us to remove the bias associated with an increasing rest-frame selection frequency with redshift. We investigate the difference this selection makes to correlations of radio source properties with redshift and luminosity by comparing the results from traditional flux-density selection with our new method. We show in particular that flux-density-based selection leads to an overestimate of the steepness of the correlation of radio source size with redshift.     

Catalog of isolated galaxies selected from the 2MASS survey

We search for isolated galaxies based on the automatic identification of isolated sources from the Two Micron All-Sky Survey (2MASS) followed by a visual inspection of their surroundings. We use the modified Karachentseva criterion to compile a catalog of 3227 isolated galaxies (2MIG), which contains 6% of 2MASS Extended Sources Catalog (or 2MASX) sources brighter than K _s = 12 ^m with angular diameters a _K ≥ 30″. The catalog covers the entire sky and has an effective depth of z ∼ 0.02. The 2493 very isolated objects of the catalog, which we include into the 2MVIG catalog, can be used as a reference sample to investigate the effects of the environment on the structure and evolution of galaxies located in regions with extremely low density of matter.     

Ultra-flat galaxies selected from RFGC catalog. I. The sample properties

We used the Revised Flat Galaxy Catalog (RFGC) to create a sample of ultra-flat galaxies (UFG) covering the whole northern and southern sky apart from theMilkyWay zone. It contains 817 spiral galaxies seen edge-on, selected into theUFG sample according to their apparent axial ratios (a/b)_B ≥ 10.0 and (a/b)_R ≥ 8.53 in the blue and red bands, respectively. Within this basic sample we fixed an exemplary sample of 441 UFG galaxies having the radial velocities of V_LG < 10000 km s^?1, Galactic latitude of | b |> 10° and the blue angular diameter of a_B > 1.′0. According to the Schmidt test the exemplary sample of 441 galaxies is characterized by about (80–90)% completeness, what is quite enough to study different properties of the ultra-flat galaxies. We found that more than 3/4 of UFGs have the morphological types within the narrow range of T = 7± 1, i.e. the thinnest stellar disks occur among the Scd, Sd, and Sdm types. The average surface brightness of UFG galaxies tends to diminish towards the flattest bulge-less galaxies. Regularly shaped disks without signs of asymmetrymake up about 2/3 both among all the RFGC galaxies, and the UFG sample objects. About 60% of ultra-flat galaxies can be referred to dynamically isolated objects, while 30% of them probably belong to the scattered associations (filaments, walls), and only about 10% of them are dynamically dominating galaxies with respect to their neighbours.     

An optical spectroscopic HR diagram for low-mass stars and brown dwarfs in Orion

The masses and temperatures of young low-mass stars and brown dwarfs in star-forming regions are not yet well established because of uncertainties in the age of individual objects and the spectral type–temperature scale appropriate for objects with ages of only a few Myr. Using multi-object optical spectroscopy, 45 low-mass stars and brown dwarfs in the Trapezium Cluster in Orion have been classified and 44 of these confirmed as bona fide cluster members. The spectral types obtained have been converted to effective temperatures using a temperature scale intermediate between those of dwarfs and giants, which is suitable for young pre-main-sequence objects. The objects have been placed on a Hertzsprung–Russell (HR) diagram overlaid with theoretical isochrones. The low-mass stars and the higher mass substellar objects are found to be clustered around the 1 Myr isochrone, while many of the lower mass substellar objects are located well above this isochrone. An average age of 1 Myr is found for the majority of the objects. Assuming coevality of the sources and an average age of 1 Myr, the masses of the objects have been estimated and range from  0.018 to 0.44 M_⊙  . The spectra also allow an investigation of the surface gravity of the objects by measurement of the sodium doublet equivalent width. With one possible exception, all objects have low gravities, in line with young ages, and the Na indices for the Trapezium objects lie systematically below those of young stars and brown dwarfs in Chamaeleon, suggesting that the 820 nm Na index may provide a sensitive means of estimating ages in young clusters.     

The X-ray spectra of optically selected Seyfert 2 galaxies: are there any Seyfert 2 galaxies with no absorption?

We present an X-ray spectral analysis of a sample of eight bona fide Seyfert 2 galaxies, selected on the basis of their high [O  iii ] λ 5007 flux, from the Ho et al. spectroscopic sample of nearby galaxies. We find that, in general, the X-ray spectra of our Seyfert 2 galaxies are complex, with some of our objects having spectra different from the 'typical' spectrum of X-ray selected Seyfert 2 galaxies. Two (NGC 3147 and 4698) show no evidence for intrinsic absorption. We suggest that this is a result of the fact that when the torus suppresses the intrinsic medium and hard energy flux, underlying emission from the host galaxy, originating in circumnuclear starbursts, and scattering from warm absorbers contributes in these energy bands more significantly. Our ASCA data alone cannot discriminate whether low-absorption objects are Compton-thick active galactic nuclei (AGNs) with a strong scattered component or lack an obscuring torus. The most striking example of our low absorption Seyfert 2 is NGC 4698. Its spectrum could be explained by either a dusty warm absorber or a lack of broad-line clouds so that its appearance as a Seyfert 2 is intrinsic and not a result of absorption.