Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
? Indi Ba, Bb: a detailed study of the nearest known brown dwarfs
The discovery of ? Indi Ba, Bb, a binary brown dwarf system veryclose to the Sun, makes possible a concerted campaign to characterisethe physical parameters of two T dwarfs. Recent observations suggestsubstellar atmospheric and evolutionary models may be inconsistent withobservations, but there have been few conclusive tests to date. Wetherefore aim to characterise these benchmark brown dwarfs to placeconstraints on such models. We have obtained high angular resolutionoptical, near-infrared, and thermal-infrared imaging andmedium-resolution (up to R ~ 5000) spectroscopy of ? Indi Ba, Bbwith the ESO VLT and present VRIzJHKL'M' broad-band photometry and0.63-5.1 ?m spectroscopy of the individual components. The photometryand spectroscopy of the two partially blended sources were extractedwith a custom algorithm. Furthermore, we use deep AO-imaging to placeupper limits on the (model-dependent) mass of any further systemmembers. We derive luminosities of log L/L? = -4.699±0.017 and -5.232 ±0.020 for ? Indi Ba, Bb,respectively, and using the dynamical system mass and COND03evolutionary models predict a system age of 3.7-4.3 Gyr, in excess ofprevious estimates and recent predictions from observations of thesebrown dwarfs. Moreover, the effective temperatures of 1352-1385 K and976-1011 K predicted from the COND03 evolutionary models, for ?Indi Ba and Bb respectively, are in disagreement with those derived fromthe comparison of our data with the BT-Settl atmospheric models where wefind effective temperatures of 1300-1340 K and 880-940 K, for ?Indi Ba and Bb respectively, with surface gravities of log g = 5.25 and5.50. Finally, we show that spectroscopically determined effectivetemperatures and surface gravities for ultra-cool dwarfs can lead tounderestimated masses even where precise luminosity constraints areavailable.Based on observations collected with the ESO VLT, Paranal, Chile underprogram 072.C-0689The full resolution spectra of both brown dwarfs are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/510/A99
| High-resolution polarimetry of Parsamian 21: revealing the structure of an edge-on FUOri disc
We present the first high spatial resolution near-infrared direct andpolarimetric observations of Parsamian 21, obtained with the NasmythAdaptive Optics System-CONICA instrument at the Very Large Telescope(VLT). We complemented these measurements with archival infraredobservations, such as Hubble Space Telescope (HST)/Wide Field PlanetaryCamera 2 (WFPC2) imaging, HST/Near Infrared Camera and Multi-ObjectSpectrometer (NICMOS) polarimetry, photometry with the Spitzer SpaceTelescope's Infrared Array Camera (IRAC) and Multiband ImagingPhotometer (MIPS), spectroscopy with Spitzer's Infrared Spectrograph(IRS), as well as Infrared Space Observatory (ISO) photometry. Our mainconclusions are as follows: (1) we argue that Parsamian 21 is probablyan FUOrionis-type object (FUor); (2) Parsamian 21 is not associated withany rich cluster of young stars; (3) our measurements reveal acircumstellar envelope, a polar cavity and an edge-on disc; the discseems to be geometrically flat and extends from approximately 48 to 360au from the star; (4) the spectral energy distribution (SED) can bereproduced with a simple model of a circumstellar disc and an envelope;(5) within the framework of an evolutionary sequence of FUors proposedby Green et al. and Quanz et al., Parsamian 21 can be classified as anintermediate-aged object.The results published in this paper are based on data collected at theEuropean Southern Observatory in the frame of the programmeP073.C-0721(A).E-mail: kospal@konkoly.hu
| The AU Microscopii Debris Disk: Multiwavelength Imaging and Modeling
Debris disks around main-sequence stars are produced by the destructionof unseen parent bodies. AU Microscopii (GJ 803) is a compelling objectto study in the context of disk evolution across different spectraltypes, as it is an M dwarf whose nearly edge-on disk may be directlycompared to that of its A5 V sibling ? Pic. We resolve the diskfrom 8-60 AU in the near-IR JHK' bands at high resolution with the KeckII Telescope and adaptive optics, and develop a data reduction techniquefor the removal of the stellar point-spread function. We measure a bluecolor across the near-IR bands, and confirm the presence of substructurein the inner disk. Some of the structural features exhibitwavelength-dependent positions. Recent measurements of thescattered-light polarization indicate the presence of porous grains. Thescattering properties of these porous grains have a strong effect on theinferred structure of the disk relative to the majority of previouslymodeled grain types. Complementing prior work, we use a Monte Carloradiative transfer code to compare a relatively simple model of thedistribution of porous grains to a broad data set, simultaneouslyfitting midplane surface brightness profiles and the spectral energydistribution. Our model confirms that the large-scale architecture ofthe disk is consistent with detailed models of steady state graindynamics. A belt of parent bodies from 35-40 AU produces dust that isthen swept outward by stellar wind and radiation. We infer the presenceof very small grains in the region exterior to the belt, down to sizesof ~0.05 ?m. These sizes are consistent with stellar mass-loss ratesM?*<<102 M?solar
| Fe II/Mg II Emission-Line Ratio in High-Redshift Quasars
We present results of the analysis of near-infrared spectroscopicobservations of six high-redshift quasars (z>~4), emphasizing themeasurement of the ultraviolet Fe II/Mg II emission-line strength toestimate the beginning of intense star formation in the early universe.To investigate the evolution of the Fe II/Mg II ratio over a wider rangein cosmic time, we measured this ratio for composite quasar spectra thatcover a redshift range 0<~z<~5 with nearly constant luminosity, aswell as for those that span ~6 orders of magnitude in luminosity. Adetailed comparison of the high-redshift quasar spectra with those oflow-redshift quasars with comparable luminosity shows essentially thesame Fe II/Mg II emission ratios and very similar continuum and linespectral properties, i.e., a lack of evolution of the relativeiron-to-magnesium abundance of the gas in bright quasars since z~=5.Current nucleosynthesis and stellar evolution models predict thatα-elements such as magnesium are produced in massive stars endingin Type II supernovae, while iron is formed predominantly in Type Iasupernovae with intermediate-mass progenitors. This results in an ironenrichment delay of ~0.2-0.6 Gyr. We conclude that intense starformation activity in the host galaxies of z>~4 quasars must havestarted already at an epoch corresponding to zf~=6-9, whenthe age of the universe was ~0.5 Gyr (H0=72 km s-1Mpc-1, ΩM=0.3,ΩΛ=0.7). This epoch corresponds well to thereionization era of the universe.Based on observations collected at the Cerro Tololo Inter-AmericanObservatory, Chile, at the European Southern Observatory, Paranal,Chile, and the W. M. Keck Observatory, Hawaii.
| VLT 3-5 micron spectroscopy and imaging of NGC 1068: Does the AGN hide nuclear starburst activity?
Near-infrared 3-5 micron spectroscopic and imaging observations of NGC1068 have been obtained with the VLT at an angular resolution of \ap 0.4arcsec. The [L-M] color index has been derived as a function of distanceto the central source of the AGN and found to show significantvariations. In particular, there is a blue excess of 0.2 mag in thevicinity of the dust/molecular torus. The 3.28 \mic polycyclic aromatichydrocarbon (PAH) emission feature has been tentatively detected towardthe central 70 pc of the AGN, with a luminosity of 7.4x 1039erg s-1. PAH emission is thought to be a strong indicator ofnuclear starburst activity. Using the measured PAH 3.28 \mic flux weestimate that the nuclear starburst activity in NGC 1068 may contributeup to 1 percent of the total infrared luminosity. Such a very smallcontribution is supported by the measured equivalent width of the PAH3.28 \mic emission feature, 1.2 nm, which is one hundred times smallerthan for starburst-dominated galaxies. Absorption features at 3.4 \mic,corresponding to carbonaceous dust have also been clearly identifiedyielding an optical depth value of tau 3.4=0.14. From this wederive an extinction of AV=28 mag toward the central source.The temperature and mass of the hot dust present in the inner 200parsecs of the central source are estimated from the L- and M-bandphotometry. For an average temperature of Tgrain ~ 475 K, wefind Mhot dust ~ 0.6 Msun. Barely detected and atL band only, the contribution of the kilo-parsec-scale ring of starformation is found to be negligible in the 3-5 ? m domain.Based on observations collected at the European Southern Observatory,Paranal, Chile, (ESO Programme 67.B-0332).
| High-Redshift Quasars and Star Formation in the Early Universe
In order to derive information on the star formation history in theearly universe, we observed six high-redshift (z~=3.4) quasars in thenear-infrared to measure the relative iron and Mg II emission strengths.A detailed comparison of the resulting spectra with those oflow-redshift quasars show essentially the same Fe II /Mg II emissionratios and very similar continuum and line spectral properties,indicating a lack of evolution of the relative iron to magnesiumabundance of the gas since z~=3.4 in bright quasars. On the basis ofcurrent chemical evolution scenarios of galaxies, where magnesium isproduced in massive stars ending in Type II Supernovae (SNe II), whileiron is formed predominantly in SNe Ia with a delay of ~1 Gyr andassuming as cosmological parameters H0=72 km s-1Mpc-1, ΩM=0.3, andΩΛ=0.7, we conclude that major star formationactivity in the host galaxies of our z~=3.4 quasars must have startedalready at an epoch corresponding to zf~=10, when the age ofthe universe was less than 0.5 Gyr. Based on observations collected atthe European Southern Observatory, La Silla, Chile.
| 2 Micron Narrowband Adaptive Optics Imaging in the Arches Cluster
Canada-France-Hawaii-Telescope adaptive optics bonnette images throughnarrowband filters in the K band are presented for the Arches cluster.Continuum fluxes, line fluxes, and equivalent widths are derived fromhigh angular resolution images, some nearly diffraction limited, for thewell-known massive stars in the Arches cluster. Images were obtained inthe lines He I 2.06 μm, H I Brγ (2.17 μm), and He II 2.19μm, as well as continuum positions at 2.03, 2.14, and 2.26 μm. Inaddition, fluxes are presented for H I Pα (1.87 μm) and anearby continuum position (1.90 μm) from Hubble Space Telescopearchival data.2 The 2 μm and Pαdata reveal two new emission-line stars and three fainter candidateemission-line objects. Indications for a spectral change of one objectbetween earlier observations in 1992-1993 and our data from 1999 arefound. The ratio of He II 2.19 μm to Brγ emission exhibits anarrow distribution among the stars, suggesting a narrow evolutionaryspread centered predominantly on spectral types O4 If or Wolf-Rayetstars of the WN7 subtype. From the approximate spectral types of theidentified emission-line stars and comparisons with evolutionary modelswe infer a cluster age between ~2 and 4.5 Myr.
| Imaging the host galaxies of high-redshift radio-quiet QSOs
We present new deep K-band and optical images of four radio-quiet QSOsat z approximately = 1 and six radio-quiet QSOs at z approximately =2.5, as well as optical images only of six more at z approximately =2.5. We have examined the images carefully for evidence of extended'fuzz' from any putative QSO host galaxy. None of the z approximately =2.5 QSOs shows any extended emission, and only two of the zapproximately = 1 QSOs show marginal evidence for extended emission. Our3 sigma detection limits in the K images, mK approximately =21 for an isolated source, would correspond approximately to anunevolved Lstar elliptical galaxy at z = 2.5 or 2-3 magfainter than an Lstar elliptical at z = 1, although ourlimits on host galaxy light are weaker than this due to the difficultyof separating galaxy light from QSO light. We simulate simple models ofdisk and elliptical host galaxies, and find that the marginal emissionaround the two z approximately = 1 QSOs can be explained by disks orbulges that are approximately 1-2 mag brighter than an unevolvedLstar galaxy in one case and approximately 1.5-2.5 magbrighter than Lstar in the other. For two other zapproximately = 1 QSOs, we have only upper limits (L approximately =Lstar). The hosts of the high-redshift sample must be nobrighter than about 3 mag above an unevolved Lstar galaxy,and are at least 1 magnitude fainter than the hosts of radio-loud QSOsat the same redshift. If the easily detected K-band light surrounding aprevious sample of otherwise similar but radio-loud QSOs is starlight,then it must evolve on timescales of greater than or approximately equalto 108 yr (e.g., Chambers & Charlot 1990); therefore ournon-detection of host galaxy fuzz around radio-quiet QSOs supports theview that high-redshift radio-quiet and radio-loud QSOs inhabitdifferent host objects, rather than being single types of objects thatturn their radio emission on and off over short timescales. This isconsistent with the general trend at low redshifts that radio-loud QSOsare found in giant elliptical galaxies while radio-quiet QSOs are foundin less luminous disk galaxies. It also suggests that the processesresponsible for the spectacular properties of radio-loud AGNs at highredshifts might not be generally relevent to the (far more numerous)radio-quiet population.
| JHKLM standard stars in the ESO system
A list of 199 standard stars suitable for the ESO standard photometricsystem at JHKLM is given. Faint stars (although brighter than K = 7.7)to be used on larger telescopes are included. This list is based on ananalysis of all infrared photometric observations carried out at LaSilla from 1979 until 1989 inclusive. The accuracy of the data (about0.02 mag. at J, H, K, L, and M) is similar to the one achieved at SAAOand CTIO. Comparisons with these systems, as well as with the AAO andMSSO systems, are made: it is shown that the ESO system is very close tothe other ones, with the exception of CTIOs.
| Southern JHKL standards
The basis for the current SAAO standard photometric system at JHKL isgiven. This depends on an extensive investigation involving 230 starsdistributed around the sky. The accuracy is estimated at + or - 0.02 magfor J, H and K and + or - 0.05 mag for L.
| Infrared standard stars
The results of an observational program aimed at setting up a network offaint near-infrared standards of sufficient accuracy are reported. Thenetwork covers both northern and southern hemispheres and includesstandards red enough to provide at least a limited check on colortransformations. The standards are set up at J (1.2 micron), H (1.6micron), K (2.2 microns), and L (3.5 microns), and their H2O and COmolecular absorption indices are determined. The problem of colortransformations between observatories is discussed briefly. Allmagnitudes presented are transformed to the natural system defined bythe CIT observations.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Turna Kusu |
| Sað Açýklýk: | 21h38m41.47s |
| Yükselim: | -41°02'52.2" |
| Görünürdeki Parlaklýk: | 8.105 |
| Uzaklýk: | 137.931 parsek |
| özdevim Sað Açýklýk: | 21.9 |
| özdevim Yükselim: | 1.6 |
| B-T magnitude: | 8.37 |
| V-T magnitude: | 8.127 |
Kataloglar ve belirtme:
|
INHABITED SKY
