Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
Are red 2MASS QSOs young?
We use photometric data from the Spitzer mission to explore the mid- andfar-infrared properties of 10 red QSOs (J - K > 2, R - K > 5mag)selected by combining the Two Micron All Sky Survey (2MASS) in thenear-infrared with the Sloan Digital Sky Survey (SDSS) at opticalwavelengths. Optical and/or near-infrared spectra are available for 8/10sources. Modelling the spectral energy distribution (SED) fromultraviolet to far-infrared shows that moderate dust reddening(AV = 1.3-3.2) can explain the red optical and near-IRcolours of the sources in the sample. There is also evidence that redQSOs have 60/12?m luminosity ratio higher than PG QSOs (97 per centsignificance). This can be interpreted as a higher level of starformation in these systems (measured by the 60-?m luminosity) for agiven active galactic nucleus (AGN) power (approximated by the 12-?mluminosity). This is consistent with a picture where red QSOs representan early phase of AGN evolution, when the supermassive black hole isenshrouded in dust and gas clouds, which will eventually be blown out(possibly by AGN driven outflows) and the system will appear as typicaloptically luminous QSO. There is also tentative evidence significant atthe 96 per cent level that red 2MASS QSOs are more often associated withradio emission than optically selected SDSS QSOs. This may indicateoutflows, also consistent with the young AGN interpretation. We alsoestimate the space density of red QSOs relative to optically selectedSDSS QSOs, taking into account the effect of dust extinction and theintrinsic luminosity of the sources. We estimate that the fraction ofred QSOs in the overall population increases from 3 per cent atMK = -27.5mag to 12 per cent at MK = -29.5mag.This suggests that reddened QSOs become more important at the bright endof the luminosity function. If red QSOs are transition objects on theway to becoming typical optically luminous QSOs, the low fractions abovesuggest that these systems spent less than 12 per cent of their lifetimeat the `reddened' stage.
| Abundances and Depletions of Interstellar Oxygen
We report on the abundance of interstellar neutral oxygen (O I) for 26sight lines, using data from the Far Ultraviolet Spectroscopic Explorer,the International Spectroscopic Explorer, and the Hubble SpaceTelescope. O I column densities are derived by measuring the equivalentwidths of several ultraviolet absorption lines and subsequently fittingthose to a curve of growth. We consider both our general sample of 26sight lines and a more restrictive sample of 10 sight lines that utilizeHST data for a measurement of the weak 1355 Å line of oxygen andare thus better constrained owing to our sampling of all three sectionsof the curve of growth. The column densities of our HST sample showratios of O/H that agree with the current best solar value if dust isconsidered, with the possible exception of one sight line (HD 37903). Wenote some very limited evidence in the HST sample for trends ofincreasing depletion with respect to RV and f(H2),but the trends are not conclusive. Unlike a recent result from Cartledgeet al., we do not see evidence for increasing depletion with respect to, but our HST sample contains only two points moredense than the critical density determined in that paper. The columndensities of our more general sample show some scatter in O/H, but mostagree with the solar value to within errors. We discuss these results inthe context of establishing the best method for determining interstellarabundances, the unresolved question of the best value for O/H in theinterstellar medium, the O/H ratios observed in Galactic stars, and thedepletion of gas-phase oxygen onto dust grains.
| Integral field spectroscopy with the GEMINI multiobject spectrographs
We describe the integral field unit (IFU) which converts the GeminiMultiobject Spectrograph (GMOS) installed on the Gemini-North telescopeto an integral field spectrograph,which produces spectra over acontiguous field of view of 7 × 5 arcsec with spatial sampling of0.2 arcsecover the wavelength range 0.4-1.0 ?m.GMOS is converted tothis mode by the remote insertion of the IFU into thebeam in place ofthe masks used for the multiobject mode. A separate fieldof half thearea of the main field, but otherwise identical, is alsoprovided toimprove background subtraction. The IFU contains 1500lenslet-coupledfibres and was the first facility of any type for integralfieldspectroscopy employed on an 8/10 m telescope.We describe the design,construction and testing of the GMOS IFU and present measurements of thethroughput both in the laboratory and at the telescope. We compare thesewith a theoretical prediction made before construction started. All arein good agreement with each other, with the on-telescope throughputexceeding 60% (averaged over wavelength). Finallywe show an example ofdata obtained during commissioning to illustrate the power of thedevice.
| VLT-spectropolarimetry of the high-polarization Seyfert 1 galaxy Fairall 51
We present high-precision optical spectropolarimetry of the Seyfert 1galaxy Fairall 51 (F51) taken with FORS1 at the VLT.The observed spectrum shows unpolarized and linearly polarizedcomponents. The AGN continuum and the broad lines show (after correctionfor the Galactic interstellar polarization and the light contribution ofthe F51 host galaxy) a practically identical amountof intrinsic polarization ranging from 5% in the red to 13% in the UV.The narrow lines are unpolarized or show only little intrinsicpolarization. The observed AGN continuum and the broad line radiationcan be explained by a combination of reddened (and attenuated) directlight and scattered light reflected from an optically thin dust region.Hence, within the framework of the unification scheme of AGN, theSeyfert 1 galaxy F51 appears to be an example of aborderline Seyfert 1/Seyfert 2 case where the nucleus is partiallyobscured like for other type 1 AGN with high intrinsic scatteringpolarization. It is found that the scattering region inF51 is located far from the BLR and the continuumsource. Thanks to this special scattering configuration, we were able tostudy the kinematics (line profiles) of the broad line region from twodifferent viewing angles, one along the line of sight (in total light)and one via the scattering region (in polarized light). The lineprofiles in polarized and total light are found to be indistinguishableto a very high accuracy, strongly indicating that the velocity field ofthe F51 BLR is essentially spherically symmetric.Based on observations obtained at the ESO VLT UT1 (Antu) at CerroParanal, Chile (ESO program 63.P-0074).
| Erreurs relevées dans le Catalogue Index 1961. 0
Not Available
| Optical and radio observations of the binary pulsar 1855 + 09 - Evolution of pulsar magnetic fields and low-mass white dwarf cooling
New radio and optical observations of the 5.4 ms binary pulsar 1855 + 09are reported. The visual extinction of the system is shown to be about1.5 mag. Only one star brighter than R about 24.6 is found that, on thebasis of positional coincidence, can be plausibly the opticalcounterpart of the secondary star. The spectrum of this candidate isinconsistent with a low-mass main-sequence star. Neither is it a whitedwarf because the spectroscopic distance modulus is inconsistent withthe lower limit on distance obtained from timing observations. It isconcluded that the companion of PSR 1855 + 09 must be a low-mass coldwhite dwarf. The inferred cooling age supports the hypothesis thatmagnetic field strengths of millisecond pulsars are essentially constantand that millisecond pulsars are long-lived objects.
| Common proper motion stars in the AGK 3
A search was made of common-proper-motion (CPM) systems among AGK 3stars. The selection of physical systems was based upon the ratiobetween the angular separation (rho) and the proper motion (mu); the CPMstars found are presented in two tables. Table I lists systems withrho/mu less than 1000 years. It contains 326 entries, and the proportionof optical pairs is estimated to be 1 percent. Table II lists systemswith rho/mu in the range 1000 to 3500 years; it contains 113 systems,but only 60 percent of them are physical. Nevertheless, these systemsoften have separations larger than 10,000 AU and are the mostinteresting for the study of the tail of the distribution function ofthe semimajor axes.
| Colors, luminosities, and motions of the nearer G-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1964AJ.....69..570E&db_key=AST
| A list of stars with common proper motions.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1958AJ.....63..246V&db_key=AST
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
| Constelación: | Boyero |
| Ascensión Recta: | 15h12m45.93s |
| Declinación: | +27°55'14.0" |
| Magnitud Aparente: | 9.38 |
| Movimiento Propio en Ascensión Recta: | 8.5 |
| Movimiento Propio en Declinación: | -131.5 |
| B-T magnitude: | 10.305 |
| V-T magnitude: | 9.457 |
Catálogos y designaciones:
|
