A study of the compact group of galaxies Shahbazian 4

The radial velocities of members of Shakhbazian 4 are determined. It is found that the dispersion of the radial velocities is 440 km/s. The apparent and absolute magnitudes of galaxies in V color are obtained. It is found that the M/L ratio of the group is about 220 solar mass/solar luminosity. The crossing time for the Shakhbazian 4 group is equal to 47 Myr

Automatic detection of arcs and arclets formed by gravitational lensing

We present an algorithm developed particularly to detect gravitationally lensed arcs in clusters of galaxies. This algorithm is suited for automated surveys as well as individual arc detections. New methods are used for image smoothing and source detection. The smoothing is performed by so-called anisotropic diffusion, which maintains the shape of the arcs and does not disperse them. The algorithm is much more efficient in detecting arcs than other source finding algorithms and the detection by eye.Comment: A&A in press, 12 pages, 16 figure

Hubble Space Telescope Planetary Camera Images of NGC 1316

We present HST Planetary Camera V and I~band images of the central region of the peculiar giant elliptical galaxy NGC 1316. The inner profile is well fit by a nonisothermal core model with a core radius of 0.41" +/- 0.02" (34 pc). At an assumed distance of 16.9 Mpc, the deprojected luminosity density reaches \sim 2.0 \times 10^3 L_{\sun} pc$^{-3}$. Outside the inner two or three arcseconds, a constant mass-to-light ratio of $\sim 2.2 \pm 0.2$ is found to fit the observed line width measurements. The line width measurements of the center indicate the existence of either a central dark object of mass 2 \times 10^9 M_{\sun}, an increase in the stellar mass-to-light ratio by at least a factor of two for the inner few arcseconds, or perhaps increasing radial orbit anisotropy towards the center. The mass-to-light ratio run in the center of NGC 1316 resembles that of many other giant ellipticals, some of which are known from other evidence to harbor central massive dark objects (MDO's). We also examine twenty globular clusters associated with NGC 1316 and report their brightnesses, colors, and limits on tidal radii. The brightest cluster has a luminosity of 9.9 \times 10^6 L_{\sun} ($M_V = -12.7$), and the faintest detectable cluster has a luminosity of 2.4 \times 10^5 L_{\sun} ($M_V = -8.6$). The globular clusters are just barely resolved, but their core radii are too small to be measured. The tidal radii in this region appear to be $\le$ 35 pc. Although this galaxy seems to have undergone a substantial merger in the recent past, young globular clusters are not detected.Comment: 21 pages, latex, postscript figures available at ftp://delphi.umd.edu/pub/outgoing/eshaya/fornax

Schwarzschild black hole lensing

We study strong gravitational lensing due to a Schwarzschild black hole. Apart from the primary and the secondary images we find a sequence of images on both sides of the optic axis; we call them {\em relativistic images}. These images are formed due to large bending of light near r = 3M (the closest distance of approach r_o is greater than 3M). The sources of the entire universe are mapped in the vicinity of the black hole by these images. For the case of the Galactic supermassive ``black hole'' they are formed at about 17 microarcseconds from the optic axis. The relativistic images are not resolved among themselves, but they are resolved from the primary and secondary images. However the relativistic images are very much demagnified unless the observer, lens and source are very highly aligned. Due to this and some other difficulties the observation of these images does not seem to be feasible in near future. However, it would be a great success of the general theory of relativity in a strong gravitational field if they ever were observed and it would also give an upper bound, r_o = 3.21 M, to the compactness of the lens, which would support the black hole interpretation of the lensing object.Comment: RevTex, 5 eps files are included, observational difficulties are discussed and there are some changes in presentatio

UX Monocerotis as a W Serpentis binary

Using our new photometric and spectroscopic observations as well as all available published data, we present a new interpretation of the properties of the peculiar emission-line binary UX Mon. We conclude that this binary is in a rare phase of fast mass transfer between the binary components prior to the mass ratio reversal. We firmly establish that the orbital period is secularly decreasing at a rate of $\dot{P}=-0.260$ seconds per year. From several lines of reasoning, we show that the mass ratio of the component losing mass to the mass-gaining component $q$ must be larger than 1 and find our most probable value to be $q=1.15\pm0.1$. The BINSYN suite of programs and the steepest descent method were used to perform the final modeling. We modeled the star as a W Ser star with a thick disk around its primary. Although the remaining uncertainties in some of the basic physical elements describing the system in our model are not negligible, the model is in fair agreement with available observations. Only the nature of the light variations outside the primary eclipse remains unexplained

Arc Statistics in Clusters: Galaxy Contribution

The frequency with which background galaxies appear as long arcs as a result of gravitational lensing by foreground clusters of galaxies has recently been found to be a very sensitive probe of cosmological models by Bartelmann et al. (1998). They have found that such arcs would be expected far less frequently than observed (by an order of magnitude) in the currently favored model for the universe, with a large cosmological constant $\Omega_\Lambda \sim 0.7$. Here we analyze whether including the effect of cluster galaxies on the likelihood of clusters to generate long-arc images of background galaxies can change the statistics. Taking into account a variety of constraints on the properties of cluster galaxies, we find that there are not enough sufficiently massive galaxies in a cluster for them to significantly enhance the cross section of clusters to generate long arcs. We find that cluster galaxies typically enhance the cross section by only $\lesssim 15$.Comment: 19 pages, 1 figure, uses aasms4.sty, submitted to Ap

Extending the limits of globule detection -- ISOPHOT Serendipity Survey Observations of interstellar clouds

A faint $I_{\rm 170}=4$ MJysr$^{-1}$ bipolar globule was discovered with the ISOPHOT 170 $\mu$m Serendipity Survey (ISOSS). ISOSS J 20246+6541 is a cold ($T_{\rm d}\approx 14.5$ K) FIR source without an IRAS pointsource counterpart. In the Digitized Sky Survey B band it is seen as a 3\arcmin size bipolar nebulosity with an average excess surface brightness of $\approx 26$ mag/$\square$\arcsec . The CO column density distribution determined by multi-isotopic, multi-level CO measurements with the IRAM-30m telescope agrees well with the optical appearance. An average hydrogen column density of $\approx 10^{21}$cm$^{-2}$ was derived from both the FIR and CO data. Using a kinematic distance estimate of 400 pc the NLTE modelling of the CO, HCO$^+$, and CS measurements gives a peak density of $\approx 10^4$cm$^{-3}$. The multiwavelength data characterise ISOSS 20246+6541 as a representative of a class of globules which has not been discovered so far due to their small angular size and low 100$\mu$m brightness. A significant overabundance of $^{13}$CO is found $X(^{13}CO) \ge 150\times X(C^{18}O)$. This is likely due to isotope selective chemical processes.Comment: 5 pages, 3 figure

Dust-scattered X-ray halos around two Swift gamma-ray bursts: GRB 061019 and GRB 070129

Two new expanding X-ray rings were detected by the Swift XRT instrument during early follow-up observations of GRB 061019 and GRB 070129, increasing to 5 the number of dust scattering X-ray halos observed around GRBs. Although these two halos were particularly faint, a sensitive analysis can be performed that optimizes the method originally developed by Tiengo & Mereghetti (2006) to analyze dust scattering rings observed with XMM-Newton for the Swift satellite. In the case of GRB 061019, a known giant molecular cloud is identified as the one responsible for the scattering process, and its distance is accurately measured (d=940$\pm$40 pc) through the dynamics of the expanding ring. In the second case, XRT observed both the main peak of the prompt emission of GRB 070129 and the scattering halo, but the small number of detected halo photons prevents us from distinguish between different dust models.Comment: 6 pages, 8 figures; Accepted by Astronomy & Astrophysics, in pres

An X-ray absorption analysis of the high-velocity system in NGC 1275

We present an X-ray absorption analysis of the high-velocity system (HVS) in NGC 1275 using results from a deep 200 ks Chandra observation. We are able to describe the morphology of the HVS in more detail than ever before. We present an HST image for comparison, and note close correspondence between the deepest X-ray absorption and the optical absorption. A column density map of the HVS shows an average column density NH of 1x10^21 cm^-2 with a range from ~5x10^20 to 5x10^21 cm^-2. From the NH map we calculate a total mass for the absorbing gas in the HVS of (1.32+-0.05)x10^9 solar masses at solar abundance. 75 per cent of the absorbing mass is contained in the four regions of deepest absorption. We examine temperature maps produced by spectral fitting and find no direct evidence for shocked gas in the HVS. Using deprojection methods and the depth of the observed absorption, we are able to put a lower limit on the distance of the HVS from the nucleus of 57 kpc, showing that the HVS is quite separate from the body of NGC 1275.Comment: 6 pages, 5 colour figures, accepted by MNRA