Deep Optical Observations Research Articles

Hubble Space Telescope Color‐Magnitude Data for Globular Clusters. I. Transformations between STIS LP Magnitudes and WFPC2 F606W and F814W Magnitudes11Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5‐26555.

ABSTRACTWe present deep Hubble Space Telescope optical imaging observations of two Galactic globular clusters, 47 Tucanae and M15, using the Space Telescope Imaging Spectrograph (STIS) longpass (LP) filter and the Wide Field and Planetary Camera 2 (WFPC2) F606W and F814W filters. These globular clusters have very different metallicities ([Fe/H ]∼ - 0.7 dex for 47 Tuc, and [Fe/H ]∼ - 2.2 dex for M15), essentially spanning the metallicity distribution of the entire Milky Way globular cluster system, and were chosen to investigate the relationship between magnitudes in the nonstandard STIS LP system and the better characterized WFPC2 magnitudes. We determine this relationship by combining our new STIS data with archival WFPC2 data, taking care to provide a robust and reliable transformation. Examining the 47 Tuc and M15 data separately, there is no evidence for a metallicity dependence in the transformation relations. This allows us to combine the data for both clusters, and also include the stars in the Small Magellanic Cloud that lie within the field of view of the 47 Tuc images, to determine final transformations that are valid for main‐sequence stars with colors in the range 0.3≲V606− I814≲1.8. These final relations predict STIS magnitudes within 0.05 mag (1 σ) of those measured for stars in both clusters. In an , we discuss the differences between our empirical transformation relations and those predicted by synthetic photometry.

An optical counterpart to the anomalous X-ray pulsar 4U0142+61.

The energy source of the anomalous X-ray pulsars (AXPs) is not understood, hence their designation as anomalous. Unlike binary X-ray pulsars, no companions are seen, so the energy cannot be supplied by accretion of matter from a companion star. The loss of rotational energy, which powers radio pulsars, is insufficient to power AXPs. Two models are generally considered: accretion from a large disk left over from the birth process, or decay of a very strong magnetic field (10(15) G) associated with a 'magnetar'. The lack of counterparts at other wavelengths has hampered progress in our understanding of these objects. Here we report deep optical observations of the field around 4U0142+61, which is the brightest AXP in X-rays. The source has no associated supernova remnant, which, together with its spin-down timescale of approximately 10(5) yr (ref. 5), suggests that it may be relatively old. We find an object with peculiar optical colours at the position of the X-ray source, and argue that it is the optical counterpart. The optical emission is too faint to admit the presence of a large accretion disk, but may be consistent with magnetospheric emission from a magnetar.

ASCAObservations of the “Failed Cluster” of Galaxies Candidate 0806+20

We have detected X-ray emission from the primary candidate for a failed of galaxies, 0806+20, with ASCA. The hypothetical failed is described by Tucker, Tananbaum, & Remillard as a large cloud of X-ray-emitting hot gas without any visible galaxies. The ASCA X-ray image of 0806+20 shows no significant extension. The time variation of X-ray flux is not significant either. Although we cannot determine whether the spectra of 0806+20 are thermal or nonthermal, we do detect an emission-line feature around 4 keV at a 95% significance level. If we identify it with an Fe K line, which should contradict the failed hypothesis, the redshift of 0806+20 is around 0.6. Moreover, we made deep optical follow-up observations, but we could not find any clear counterparts of this X-ray source down to a magnitude limit of R ~ 24 mag. We thus conclude that 0806+20 is either a very distant cluster of galaxies (so that the individual galaxies could not be detected) or an extremely optically underluminous X-ray quasar.

Discovery of a Nearby Low Surface Brightness Spiral Galaxy

During the course of a search for compact, isolated gas clouds moving with anomalous velocities in or near our own Galaxy, we have discovered in the data of the Leiden/Dwingeloo survey of Galactic hydrogen the H I signature of a large galaxy moving at a recession velocity of 282 km s-1 with respect to our Galaxy. Deep multicolor and spectroscopic optical observations show the presence of star formation in scattered H II regions; radio H I synthesis interferometry confirms that the galaxy is rich in H I and has the rotation signature of a spiral galaxy; a submillimeter observation failed to detect the CO molecule. The radio and optical evidence combined suggest its classification as a low surface brightness (LSB) spiral galaxy. It is located in close spatial and kinematic proximity to the galaxy NGC 6946. The newly discovered galaxy, which we call Cep 1, is at a distance of about 6 Mpc. It is probably to be numbered among the nearest few LSB spiral galaxies.

COMPACT GROUPS OF GALAXIES

ABSTRACT Compact groups of galaxies typically contain fewer than ten galaxies, separated from one another on the plane of the sky by a galaxy diameter or less. A continuing question about these groups is why we see so many of them even though galaxy interactions should quickly destroy the individual galaxies and result in a single merger remnant. The presence of tidally distorted galaxies in these groups implies that they are not simply projections of unrelated galaxies on the sky. Hickson compact groups (HCGs) form a well-defined sample that can be examined for clues to this puzzle. We used deep X-ray (ROSAT PSPC) and optical observations of twelve Hickson groups to explore their interaction histories. Diffuse X-ray emission (of luminosity 1041-42 erg s-1 is seen primarily in elliptical-rich HCGs, implying that these groups contain gas at a temperature of kT ~0.9 keV. Total and gas masses obtained from the X-ray data show that these groups have baryon fractions similar to those of clusters of galaxies, but gas-to-stellar-mass ratios two orders of magnitude smaller. Deep, multicolor photometry of the same sample shows no correlation between the presence of tidal features in group galaxies and X-ray emission in a group; however, two bright ellipticals in the sample not previously thought to be merger remnants have peculiar color structures and extremely low X-ray luminosities which may result from mergers. HCG 94 is an exceptional group: extremely X-ray-luminous, it is the only group in our sample with diffuse optical light in the group potential (the other groups have an upper limit of 1/3 L*, while the light in HCG 94 has a luminosity of 7 L*). High-resolution X-ray observations show that the diffuse hot gas and the diffuse light trace the same potential in this group, implying that this potential is changing slowly. Galaxy-formation simulations in a cold-dark-matter-dominated universe create groups that have properties similar to X-ray-bright HCGs; however, the simulated groups are not physically compact for most of the time that they are X-ray-luminous.

Optical identification of X- and gamma-ray sources: the use of existing data

We briefly discuss the use of existing astronomical data, mainly deep optical observations performed in order to obtain galaxy and star counts, for the identification of gamma-ray burst sources in particular and of newly discovered X- and gamma-ray sources in general. Use of such data cannot only reduce the amount of required telescope time but also, in comparison with present-day observations, allow the search for variability and proper motion of candidate optical counterparts over a time span of several years.

The Parkes Selected Regions: deep optical and infrared observations of radio galaxies and quasars at high redshifts

Les resultats d'une etude optique et IR complete sont presentes pour les 178 radiosources dans les Regions Selectionnees Parkes (S>100 mJy a 2.7 GHz). Les observations CCD ont resulte en l'achevement du programme d'identification optique et ont fourni la photometrie B et R des nouvelles identifications. La photometrie K a ete completee pour 4 des 6 regions selectionnees. De nouvelles observations spectroscopiques ont renforce le contenu en redshift a 46%, incluant tous les candidats quasars. L'estimation du redshift est discutee pour les radiogalaxies restantes dans le contexte de la photometrie B, R et K

Extragalactic sources with asymmetric radio structure II. further observations of the quasar B2 1320 + 299

We present VLA A-array observations at λ20, 6 and 2 cm and B-array observations at λ20 and 6 cm of the quasar B2 1320 + 299, which has a very unusual radio structure. In addition to a component, A, coincident with the quasar, there are two lobes of radio emission, B and C, on the same side of A. These are located at distances of -25 and 50 arcsec respectively from A. The present observations show that A has a flat-spectrum component coincident with the quasar and a weak outer component at a distance of-4 arcsec along PA - 100°. The morphology of B resembles a head-tail type of structure with its tail towards the north-east. The magnetic field lines in component B appear to follow the bend in the tail. Component C exhibits some extension towards the north-west. We discuss the possible nature of B2 1320 + 299 and suggest that while A appears to be an independent source, the relation between B and C, if they are associated at all, is unclear. Deep optical observations are essential to help clarify the situation.

Deep optical and radio observations of the gravitational lens system 2016 + 112

view Abstract Citations (43) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Deep optical and radio observations of the gravitational lens system 2016+112. Schneider, D. P. ; Lawrence, C. R. ; Schmidt, M. ; Gunn, J. E. ; Turner, E. L. ; Burke, B. F. ; Dhawan, V. Abstract New optical and radio observations of the gravitational lens system 2016 + 112 are presented. Deep optical images reveal the presence of an extremely red galaxy located in the midst of the three radio positions. There is no evidence for a cluster of galaxies in the region; the lensing appears to be dominated by the new galaxy and the galaxy associated with the third radio source. The A image has remained constant in brightness since its discovery nearly a year ago, but B has faded by about 0.3 mag. A new spectrum of B shows that the equivalent widths of its emission lines have increased by roughly a factor of 2. A wide-field radio map shows that the postulated third image must either be more than 100 times fainter than A and B, or else lie close to one of the detected radio sources. The discovery of the new lensing mass makes the geometry of this lens system somewhat easier to understand, but no model based only on idealized mass distributions at the locations of the two known galaxies can explain all the observed properties. Publication: The Astrophysical Journal Pub Date: July 1985 DOI: 10.1086/163275 Bibcode: 1985ApJ...294...66S Keywords: Astronomical Photography; Astronomical Spectroscopy; Galactic Clusters; Gravitational Lenses; Quasars; Radio Astronomy; Charge Coupled Devices; Astrophysics full text sources ADS | data products SIMBAD (3) NED (1)