Contents
Images
Upload your image
DSS Images Other Images
Related articles
Detection of Water Ice Grains on the Surface of the Circumstellar Disk Around HD 142527
Coronagraphic imaging for the Herbig Ae star, HD 142527, wasperformed using the Coronagraphic Imager with Adaptive Optics (CIAO) onthe 8.2 m Subaru Telescope. The images were obtained in theH2O ice filter (? = 3.08 ?m) using adaptive optics(AO), and in the L' band without AO. Combining these data with previousobservational results in the H and K bands, we derived the spectra ofthe scattered light from the circumstellar disk around HD 142527and detected an H2O ice absorption feature in the spectra.This result can be explained by the presence of silicate andH2O ice grains of ~1 ?m in size, according to theprediction model by Inoue et al. This grain size is consistent withprevious observational study by Fukagawa et al. and Fujiwaraet al. The present result demonstrates that high-resolution imagingof disk-scattered light in the ice band is useful for detectingH2O ice grain distributions in circumstellar disks.Based on data collected at Subaru Telescope, which is operated by theNational Astronomical Observatory of Japan.
| A multi-wavelength census of star formation activity in the young embedded cluster around Serpens/G3-G6
Aims.The aim of this paper is to characterise the star formationactivity in the poorly studied embedded cluster Serpens/G3-G6, located~45 arcmin (3 pc) to the south of the Serpens Cloud Core, and todetermine the luminosity and mass functions of its population of YoungStellar Objects (YSOs). Methods: .Multi-wavelength broadbandphotometry was obtained to sample the near and mid-IR spectral energydistributions to separate YSOs from field stars and classify the YSOevolutionary stage. ISOCAM mapping in the two filters LW2 (5-8.5 μm)and LW3 (12-18 μm) of a 19 arcmin × 16 arcmin field wascombined with JHKS data from 2MASS, KS data from Arnica/NOT,and L arcmin data from SIRCA/NOT. Continuum emission at 1.3 mm (IRAM)and 3.6 cm (VLA) was mapped to study the cloud structure and thecoldest/youngest sources. Deep narrow band imaging at the 2.12 μmS(1) line of H2 from NOTCam/NOT was obtained to search for signs ofbipolar outflows. Results: .We have strong evidence for a stellarpopulation of 31 Class II sources, 5 flat-spectrum sources, 5 Class Isources, and two Class 0 sources. Our method does not sample the ClassIII sources. The cloud is composed of two main dense clumps alignedalong a ridge over ~0.5 pc plus a starless core coinciding withabsorption features seen in the ISOCAM maps. We find two S-shapedbipolar collimated flows embedded in the NE clump, and propose the twodriving sources to be a Class 0 candidate (MMS3) and a double Class I(MMS2). For the Class II population we find a best age of ~2 Myr andcompatibility with recent Initial Mass Functions (IMFs) by comparing theobserved Class II luminosity function (LF), which is complete to 0.08Lȯ, to various model LFs with different star formationscenarios and input IMFs.
| Discovery of an Optically Thick, Edge-on Disk around the Herbig Ae Star PDS 144N
We have discovered an optically thick, edge-on circumstellar disk arounda Herbig Ae star in the binary system PDS 144, providing the firstintermediate-mass analog of HK Tau and similar T Tauri stars. Thissystem consists of a V~13 mag primary and a fainter companion, with thespectra of both stars showing evidence for circumstellar disks andaccretion; both stars were classified as Herbig Ae by the Pico dos DiasSurvey. In Lick adaptive optics polarimetry, we resolved extendedpolarized light scattered from dust around the northern star. Follow-upKeck adaptive optics and mid-infrared observations show that this staris entirely hidden by an optically thick disk at all wavelengths from1.2 to 11.7 μm. The disk major axis subtends ~0.8" on the sky,corresponding to ~800 AU at a distance of 1000 pc. Bright ``wings''extend 0.3" above and below the disk ansae, due most likely toscattering from the edges of an outflow cavity in a circumstellarenvelope. We discuss the morphology of the disk and the spectral energydistributions of the two PDS 144 stars, present preliminary disk models,and identify a number of open questions regarding this fascinatingsystem.Some of the data presented here were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.
| Calibration of the Infrared Telescope Facility National Science Foundation Camera Jupiter Galileo Data Set
The NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, setaside some time on about 500 nights from 1995 to 2002, when the NSFCAMfacility infrared camera was mounted and Jupiter was visible, for astandardized set of observations of Jupiter in support of the Galileomission. The program included observations of Jupiter, nearby referencestars, and dome flats in five filters: narrowband filters centered at1.58, 2.28, and 3.53 μm, and broader L' and M' bands that probe theatmosphere from the stratosphere to below the main cloud layer. Thereference stars were not cross-calibrated against standards. Weperformed follow-up observations to calibrate these stars and Jupiter in2003 and 2004. We present a summary of the calibration of the Galileosupport monitoring program data set. We present calibrated magnitudes ofthe six most frequently observed stars, calibrated reflectivities, andbrightness temperatures of Jupiter from 1995 to 2004, and a simplemethod of normalizing the Jovian brightness to the 2004 results. Ourstudy indicates that the NSFCAM's zero-point magnitudes were not stablefrom 1995 to early 1997, and that the best Jovian calibration possiblewith this data set is limited to about +/-10%. The raw images andcalibration data have been deposited in the Planetary Data System.
| Empirically Constrained Color-Temperature Relations. II. uvby
A new grid of theoretical color indices for the Strömgren uvbyphotometric system has been derived from MARCS model atmospheres and SSGsynthetic spectra for cool dwarf and giant stars having-3.0<=[Fe/H]<=+0.5 and 3000<=Teff<=8000 K. Atwarmer temperatures (i.e., 8000-2.0. To overcome thisproblem, the theoretical indices at intermediate and high metallicitieshave been corrected using a set of color calibrations based on fieldstars having well-determined distances from Hipparcos, accurateTeff estimates from the infrared flux method, andspectroscopic [Fe/H] values. In contrast with Paper I, star clustersplayed only a minor role in this analysis in that they provided asupplementary constraint on the color corrections for cool dwarf starswith Teff<=5500 K. They were mainly used to test thecolor-Teff relations and, encouragingly, isochrones thatemploy the transformations derived in this study are able to reproducethe observed CMDs (involving u-v, v-b, and b-y colors) for a number ofopen and globular clusters (including M67, the Hyades, and 47 Tuc)rather well. Moreover, our interpretations of such data are verysimilar, if not identical, with those given in Paper I from aconsideration of BV(RI)C observations for the sameclusters-which provides a compelling argument in support of thecolor-Teff relations that are reported in both studies. Inthe present investigation, we have also analyzed the observedStrömgren photometry for the classic Population II subdwarfs,compared our ``final'' (b-y)-Teff relationship with thosederived empirically in a number of recent studies and examined in somedetail the dependence of the m1 index on [Fe/H].Based, in part, on observations made with the Nordic Optical Telescope,operated jointly on the island of La Palma by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.Based, in part, on observations obtained with the Danish 1.54 mtelescope at the European Southern Observatory, La Silla, Chile.
| L' and M' standard stars for the Mauna Kea Observatories Near-Infrared system
We present L' and M' photometry, obtained at the United Kingdom InfraredTelescope (UKIRT) using the Mauna Kea Observatories Near-Infrared(MKO-NIR) filter set, for 46 and 31 standard stars, respectively. The L'standards include 25 from the in-house `UKIRT Bright Standards' withmagnitudes deriving from Elias et al. and observations at the InfraredTelescope Facility in the early 1980s, and 21 fainter stars. The M'magnitudes derive from the results of Sinton and Tittemore. We estimatethe average external error to be 0.015 mag for the bright L' standardsand 0.025 mag for the fainter L' standards, and 0.026 mag for the M'standards. The new results provide a network of homogeneously observedstandards, and establish reference stars for the MKO system, in thesebands. They also extend the available standards to magnitudes whichshould be faint enough to be accessible for observations with moderndetectors on large and very large telescopes.
| JHK Standard Stars on the CIT Photometric System
We present a set of 58 stars with JHK standard values on the CIT systemand with a suitable magnitude range for use with array detectors onsmall- to moderate-size telescopes. Each final value is based on six to47 measures (with a mean of 17) obtained on separate nights with the USNaval Observatory (USNO) NICMOS3 (HgCdTe) camera. The objects include 20primary CIT standards from Elias et al. and 38 secondary sourcesselected from the SAAO and UKIRT standards lists, cover a K-magnituderange between 6.0 and 10.8, and lie north of declination -20°. Thestars were reduced to the CIT system as defined by Elias et al.,producing a USNO system that is identical to the near-infrared CITsystem. This work densifies the original CIT system by nearly a factorof 3 and extends its range by about 3 mag. The SAAO and UKIRT standardsare also compared with the CIT system.
| High-Precision Near-Infrared Photometry of a Large Sample of Bright Stars Visible from the Northern Hemisphere
We present the results of 8 yr of infrared photometric monitoring of alarge sample of stars visible from Teide Observatory (Tenerife, CanaryIslands). The final archive is made up of 10,949 photometric measuresthrough a standard InSb single-channel photometer system, principally inJHK, although some stars have measures in L'. The core of this list ofstars is the standard-star list developed for the Carlos SánchezTelescope. A total of 298 stars have been observed on at least twooccasions on a system carefully linked to the zero point defined byVega. We present high-precision photometry for these stars. The medianuncertainty in magnitude for stars with a minimum of four observationsand thus reliable statistics ranges from 0.0038 mag in J to 0.0033 magin K. Many of these stars are faint enough to be observable with arraydetectors (42 are K>8) and thus to permit a linkage of the bright andfaint infrared photometric systems. We also present photometry of anadditional 25 stars for which the original measures are no longeravailable, plus photometry in L' and/or M of 36 stars from the mainlist. We calculate the mean infrared colors of main-sequence stars fromA0 V to K5 V and show that the locus of the H-K color is linearlycorrelated with J-H. The rms dispersion in the correlation between J-Hand H-K is 0.0073 mag. We use the relationship to interpolate colors forall subclasses from A0 V to K5 V. We find that K and M main-sequence andgiant stars can be separated on the color-color diagram withhigh-precision near-infrared photometry and thus that photometry canallow us to identify potential mistakes in luminosity classclassification.
| Near-Infrared Photometric Survey of Proto-planetary Nebula Candidates
We present JHK' photometric measurements of 78 objects mostly consistingof proto-planetary nebula candidates. Photometric magnitudes aredetermined by means of imaging and aperture photometry. Unlike theobservations with a photometer with a fixed-sized beam, the method ofimaging photometry permits accurate derivation of photometric values,because the target sources can be correctly identified and confusionwith neighboring sources can be easily avoided. Of the 78 sourcesobserved, we report nearly 10 cases in which the source seems to havebeen misidentified or confused by nearby bright sources. We also presentnearly two dozen cases in which the source seems to have indicated avariability that prompts a follow-up monitoring. There are also a fewsources that show previously unreported extendedness. In addition, wepresent H-band finding charts of the target sources.
| Molecular Hydrogen in the Ring Nebula: Clumpy Photodissociation Regions
We present a 0.65" resolution H2 1-0 S(1) 2.122 μm imageof the Ring Nebula (NGC 6720), which was taken with the Near InfraredImager at the WIYN 3.5 m telescope on Kitt Peak. The high resolution ofthe H2 observation is sufficient to reveal the finerstructure of the molecular material in this nebula. The morphology ofthe molecular emission is compared to that of the ionized emission fromthe Ring Nebula as seen by the Hubble Space Telescope (HST; He II, [OIII], and [N II]), and it is clear that the dark clumps seen by HSTmatch the locations of clumpy H2 emission, suggesting thatthese clumps are similar to the cometary knots seen in the Helix Nebula.As with the Helix, the clumpy H2 emission from the main ringof the Ring Nebula is contained within the optically bright ionizednebula, implying that the molecular gas is shielded inside densecondensations. Comparison of the observed H2 average surfacebrightnesses for the Ring Nebula [(1.5+/-0.5)×10-4 ergscm-2 s-1 sr-1] with time-dependentmodels of the expected H2 emission from planetary nebulae(PNe) shows that it is consistent with H2 excitation inphotodissociation regions (PDRs), confirming previous suggestions.Comparison of the Ring Nebula H2 emission with a younger PN,NGC 2346, and an older PN, the Helix Nebula, suggests an evolution inH2 surface brightness consistent with the time-dependent PDRmodels. Moreover, the knots of molecular gas appear to become moreisolated as the PN evolves, consistent with optical studies of knots inPNe.
| Astrophysics of Young Star Binaries
This paper describes our study of the astrophysics of individualcomponents in close pre-main-sequence binaries. We observed both starsin 17 systems, located in four nearby star-forming regions, usinglow-resolution (R=760) infrared spectroscopy and photometry. For 29components we detected photospheric absorption lines and were able todetermine spectral type, extinction, K-band excess, and luminosity. Theother five objects displayed featureless or pure emission line spectra.In ~50% of the systems, the extinction and K-band excess of the primarystars dominate those of the secondaries. Masses and ages were determinedfor these 29 objects by placing them on the H-R diagram, overlaid withtheoretical pre-main-sequence tracks. Most of the binaries appear to becoeval. The ages span 5×105 to 1×107yr. The derived masses range from the substellar, 0.06Msolar, to 2.5 Msolar, and the mass ratios fromM2/M1=0.04 to 1.0. Fourteen stars show evidence ofcircumstellar disks. The K-band excess is well correlated with the K-Lcolor for stars with circumstellar material.
| Near-Infrared Observations of Neptune's Tropospheric Cloud Layer with the Lick Observatory Adaptive Optics System
We provide one of the first constraints on the combined infraredsingle-scattering albedo and opacity of Neptune's upper troposphericcloud layer. For the observations, we used the adaptive optics system onthe Lick Observatory's 3 m Shane Telescope (Mount Hamilton, California).The cloud layer is thought to be composed of H2S and extendup to 3.5-4.5 bars. Previously, the single-scattering albedo wasmeasured in the range 0.2-0.94 μm and found to be extremely high(>0.8), but decreasing with increasing wavelength. Assuming an opticallythick cloud, we find the best-fit single-scattering albedo of a 3.5 barlayer to be 0.23+0.07-0.08 at 1.27 μm and0.18+0.03-0.04 at 1.56 μm. Uncertainties in thecolumn density of haze above the cloud layer, and from deconvolution toremove contaminating light scattered by the point-spread function frominfrared-bright features, indicate that the cloud could be even darker,but it is unlikely to be brighter than we report. The cloud particlescould be brighter than we report if the total near-infrared opacity ofthe cloud is very low or the cloud's scattering phase function issignificantly more forward-scattering at 1.2-1.6 μm than at 0.75μm.
| The infrared counterpart of the Z source GX 5-1
We have obtained UK Infrared Telescope infrared observations of thefield of the bright Galactic Z source GX 5-1. From an astrometric platesolution tied to Tycho-ACT standards we have obtained accurate positionsfor the stars in our field which, combined with an accurate radioposition, have allowed us to identify the probable infrared counterpartof GX 5-1. Narrow-band photometry marginally suggests excess Br?emission in the counterpart, supporting its association with anaccretion-disc source. No significant variability is observed in alimited number of observations. We compare the H and K magnitudes withthose of other Z sources, and briefly discuss possible sources ofinfrared emission in these systems.
| Do galaxy mergers form elliptical galaxies? A comparison of kinematic and photometric properties
We present near-infrared K-band imaging and spectroscopy of a sample ofgalaxy mergers, which we use to derive light profile indices, absolutemagnitudes and central velocity dispersions. We find that the lightdistributions of mergers more nearly resemble those of ellipticals thanthose of bulges, but that the mergers lie well away from the FundamentalPlane defined by the ellipticals. We interpret this as being due toenhancement of the K-band surface brightness of the mergers by asignificant population of supergiant stars, and independent evidence forsuch a population is inferred from measurements of the depth of the2.3-μm CO absorption feature.
| Excitation and kinematics in H_2 bow shocks: near-infrared observations of HH 99 and VLA 1623A (HH 313)
We present a comprehensive near-infrared study of two molecular bowshocks in two protostellar outflows, HH 99 in R Coronae Australis andVLA 1623A (HH 313) in Rho Ophiuchi. New, high-resolution, narrow-bandimages reveal the well-defined bow shock morphologies of both sources.These are compared with two-dimensional MHD modelling of molecular bowsfrom which we infer flow inclination angles, shock speeds and themagnetic field in the pre-shock gas in each system. With combinedechelle spectroscopy and low-resolution K-band spectra we furtherexamine the kinematics and excitation of each source. Bow shock modelsare used to interpret excitation (CDR) diagrams and estimate theextinction and, in the case of VLA 1623, the ortho-para ratio associatedwith the observed H_2 population. For the first time, morphology,excitation and kinematics are fitted with a single bow shock model.Specifically, we find that HH 99 is best fitted by a C-type bow shockmodel (although a J-type cap is probably responsible for the [Feii]emission). The bow is flowing away from the observer (at an angle to theline of sight of ~45 deg) at a speed of roughly 100kms^-1. VLA 1623A isinterpreted in terms of a C-type bow moving towards the observer (at anangle to the line of sight of ~75 deg) at a speed of ~80kms^-1. Themagnetic field associated with HH 99 is thought to be orientatedparallel to the flow axis; in VLA 1623A the field is probably oblique tothe flow axis, since this source is clearly asymmetric in our H_2images.
| High-Angular Resolution Millimeter-Wave and Near-Infrared Imaging of the Ultracompact H II Region G29.96-0.02
We present a high-angular resolution study of the cometary-shapedultracompact H II region G29.96-0.02. We have obtained ~10"angular-resolution millimeter-wave maps of the region in transitions of^13CO, C^18O, CH_3CN, CH_3OH, and CS with the BIMA interferometer. Wecombine these data with complementary single-dish data of the ^13CO,C^18O, and CS lines taken with the FCRAO 14 meter telescope. These dataare compared with near-infrared JHK-band images with <=0.9" angularresolution obtained with the Calar-Alto 3.5 m telescope. The ^13CO datashow emission extended over a 3x2 pc region; however, the emission isstrongly peaked near the head of the H II region. Strong CS, C^18O, andCH_3CN emissions peak near the same location. The CH_3CN (J=6-->5)emission peaks toward the hot core previously detected in VLA NH_3(4, 4)observations, and we determine a kinetic temperature of 100 K in thecore using a large velocity gradient analysis of the CH_3CN (6-->5)BIMA data and CH_3CN/CH^13_3CN (5-->4) IRAM 30 m telescope data. Wealso find that the sharply peaked C^18O, ^13CO, and CS emission isindicative of a density gradient, with the peak density located in frontof the head of the cometary H II region. We use our near-infrared datato search for sources embedded in the H II region and the adjacentcloud. In addition to the exciting star of the H II region, we identifya second star toward the head of the H II region with an extinctionsimilar to that of the exciting star; this appears to be a second OBstar in the H II region. Directly in front of the H II region we detecta highly reddened source, which is most likely a young star deeplyembedded in the molecular gas. Furthermore, we find an enhanced densityof sources with H-K >1 toward the molecular cloud and argue thatthese sources form an embedded cluster. Finally, we compare our resultswith current models of cometary shaped H II regions. Given the evidencethat the G29.96 H II region exists in a gradient of molecular gasdensity that peaks in front of the head of the H II region, we favor thechampagne flow model for this region. Comparing the measured densities,temperatures, and line widths of the ionized and molecular gas, weestimate the expansion speed of the H II region into the molecular coreat 2-5 km s^-1.
| Optical and infrared observations of the luminous quasar PDS 456: a radio-quiet analogue of 3C 273?
We present infrared photometry and optical and infrared spectroscopy ofthe recently discovered, extremely luminous nearby quasar PDS 456. Anumber of broad emission features are seen in the near-infrared, whichwe are unable to identify. We measure a more accurate redshift from anarrow forbidden emission line and compare the optical-infrared spectrumto that of 3C 273. The close similarity suggests that PDS 456 is aradio-quiet analogue of 3C 273, although radio observations do notsupport this idea.
| Towards a fundamental calibration of stellar parameters of A, F, G, K dwarfs and giants
I report on the implementation of the empirical surface brightnesstechnique using the near-infrared Johnson broadband { (V-K)} colour assuitable sampling observable aimed at providing accurate effectivetemperatures of 537 dwarfs and giants of A-F-G-K spectral-type selectedfor a flux calibration of the Infrared Space Observatory (ISO). Thesurface brightness-colour correlation is carefully calibrated using aset of high-precision angular diameters measured by moderninterferometry techniques. The stellar sizes predicted by thiscorrelation are then combined with the bolometric flux measurementsavailable for a subset of 327 ISO standard stars in order to determineone-dimensional { (T, V-K)} temperature scales of dwarfs and giants. Theresulting very tight relationships show an intrinsic scatter induced byobservational photometry and bolometric flux measurements well below thetarget accuracy of +/- 1 % required for temperature determinations ofthe ISO standards. Major improvements related to the actual directcalibration are the high-precision broadband { K} magnitudes obtainedfor this purpose and the use of Hipparcos parallaxes for dereddeningphotometric data. The temperature scale of F-G-K dwarfs shows thesmallest random errors closely consistent with those affecting theobservational photometry alone, indicating a negligible contributionfrom the component due to the bolometric flux measurements despite thewide range in metallicity for these stars. A more detailed analysisusing a subset of selected dwarfs with large metallicity gradientsstrongly supports the actual bolometric fluxes as being practicallyunaffected by the metallicity of field stars, in contrast with recentresults claiming somewhat significant effects. The temperature scale ofF-G-K giants is affected by random errors much larger than those ofdwarfs, indicating that most of the relevant component of the scattercomes from the bolometric flux measurements. Since the giants have smallmetallicities, only gravity effects become likely responsible for theincreased level of scatter. The empirical stellar temperatures withsmall model-dependent corrections are compared with the semiempiricaldata by the Infrared Flux Method (IRFM) using the large sample of 327comparison stars. One major achievement is that all empirical andsemiempirical temperature estimates of F-G-K giants and dwarfs are foundto be closely consistent between each other to within +/- 1 %. However,there is also evidence for somewhat significant differential effects.These include an average systematic shift of (2.33 +/- 0.13) % affectingthe A-type stars, the semiempirical estimates being too low by thisamount, and an additional component of scatter as significant as +/- 1 %affecting all the comparison stars. The systematic effect confirms theresults from other investigations and indicates that previousdiscrepancies in applying the IRFM to A-type stars are not yet removedby using new LTE line-blanketed model atmospheres along with the updatedabsolute flux calibration, whereas the additional random component isfound to disappear in a broadband version of the IRFM using an infraredreference flux derived from wide rather than narrow band photometricdata. Table 1 and 2 are only available in the electronic form of thispaper
| Infrared spectroscopy of Sakurai's object
We present near (ground-based) and far (ISO) infrared spectroscopy ofSakurai's object. As in the case of the optical spectrum, between 1996and 1997 April the near-infrared spectrum underwent a dramatic change tolater spectral type, and there is some evidence that the spectrumcontinued to evolve during 1997. Molecular features of carbon-bearingmolecules (CN, C_2, CO) - corresponding to those seen in cool carbonstars - are now prominent in the 1-2.5mum range, and the ^12C/^13C ratiois low. The ISO data demonstrate the presence of hot circumstellar dustat a temperature of ~680K. If the dust shell is optically thin, the dustmass is ~2.8x10^-8Msolar.
| Near-infrared star counts as a test of a Galactic bar structure
We present survey data in the narrow-band L filter (nbL), taken atUKIRT, for a total area of 277 sq arcmin, roughly equally dividedbetween four regions at zero Galactic latitude and longitudes +/- 4.3deg and +/- 2.3 deg. The 80 percent completeness level for theseobservations is at roughly magnitude 11.0. This magnitude limit, owingto the low coefficient for interstellar extinction at this wavelength,allows us to observe bulge giants. We match the nbL magnitudes withDENIS survey K magnitudes, and find 95 percent of nbL sources arematched to K sources. Constructing color-magnitude diagrams, we dereddenthe magnitudes and find evidence for a longitude-dependent asymmetry inthe source counts. We find that there are about 15 and 5 percent moresources at the negative longitude than at the corresponding positivelongitude for the fields at +/- 4.3 and +/- 2.3 deg, respectively. Thisis compared with the predictions of some Galactic bar models. We find anasymmetry in the expected sense, which favors gas dynamical models andthe recent deconvolution of surface photometry data over earliertreatments of photometric data.
| Young red supergiants and the near-infrared light appearance of disk galaxies
We have searched for spatial variations in the 2.3 m photometric COindex within the disks of three nearby galaxies. This index measures thestrength of the absorption bands of molecular CO in stellar atmospheresand is strong in cool, low surface gravity stars, reaching the largestvalues for red supergiants. We observe significant spatial CO indexvariations in two galaxies, indicating that the dominant stellarpopulation in the NIR is not everywhere the same. Central CO index peaksare present in two galaxies; these could be due to either metallicitygradients or to recent star formation activity. In addition, significantazimuthal CO index variations are observed in one. Because strongazimuthal metallicity gradients are physically implausible in diskgalaxies, these features are most naturally explained by the presence ofa young stellar population. The fraction of 2 m light due to youngstellar populations in star-forming regions can be calculated from ourdata. Overall, young stellar populations can contribute 3 percent of theNIR flux of a (normal) galaxy, which is consistent with other globalproperties. Locally, this fraction may rise to 33 percent. Thus, youngstars do not dominate the total NIR flux, but can be locally dominant instar-forming regions, and can bias estimates of spiral arm amplitude orother nonaxisymmetric structures in galaxies' mass distributions.
| The near-infrared extinction law and limits on the pre-main-sequence population of the Rho Ophiuchi dark cloud
We describe new techniques to measure the NIR extinction law and toplace limits on the premain-sequence stellar population of a dark cloud.We analyze JHK imaging data for the central 1 sq deg of the Rho Ophiuchicloud core and show that nearly all stars projected onto regions of lowCS intensity, ICS 10 K km/s, are background stars. Most sources atlarger CS intensities lie within cloud material. We use the backgroundstars to derive the slope of the NIR extinction law, E(J-H)/E(H-K) =1.57 +/- 0.03. This result is consistent with previous extinction lawsbut has a factor of two to three smaller uncertainty. The new Rho Ophextinction law yields strong constraints on the number of previouslyundiscovered premain-sequence stars in the cloud, 46 +/- 11, and thenumber of previously undiscovered young stars with near-IR excesses, 15+/- 4. Neither limit exceeds the number of known premain-sequence starsin the cloud about 100. Thus, current samples of premain-sequence starsare reasonably complete for K = 14 or less.
| Near-IR imaging photometry of NGC 1333: a 3-μm imaging survey
We combine new near-infrared 3.42-μm imaging photometry with JHK datafrom Paper I to further probe the membership and physicalcharacteristics of the embedded pre-main-sequence (PMS) population inthe active star formation region NGC 1333-S. Our new data set coversapproximately 44 per cent of the 10x10 arcmin^2 area previouslysurveyed. In the current survey region we have detected 36 sources, 26being brighter than our 5sigma limiting magnitude of m_L=12.2. These 36objects represent 45 per cent of the 80 objects detected in the sameregion at K. From a near-IR J-K versus K-L colour-colour diagram weinfer the evolutionary state of the stars and compare the results withthose obtained from our JHK data. We additionally discuss the effect of3.08-μm ice absorption on photometry at 3.42mum for heavily embeddedobjects.
| Flaring and quiescent infrared behaviour of Cygnus X-3
We present new infrared observations of the exotic X-ray binary systemCygnus X-3, including high-time-resolution simultaneous H- and K-bandphotometry over ~1.5 orbital periods and 1-5mum photometry during bothperiods of apparent infrared quiescence and flaring activity. Thesimultaneous H- and K-band observations reveal the 4.8-h orbitalmodulation of the source, superimposed upon which are a number ofextremely rapid flare events. We find rise times for these events of<=15 s, and find that the source becomes redder in (H-K) during theflares. This latter effect is confirmed by 1-5 μm photometry during aperiod of prolonged quasi-stable flaring. We model this reddening incolour during flaring in terms of optically thin free-free emission froma hot dense plasma, possibly associated with a thermal gas in thehigh-velocity radio jets revealed by radio VLBI. Size, luminosity andlack of self-absorption considerations allow us to place strongconstraints on possible values of N_e and T for this plasma, and we findthat the dominant cooling mechanism is likely to be bremsstrahlungcooling. Dereddening of new 1-5mum data combined with 0.7-1.0mum resultsfrom the literature is consistent with an estimated infrared extinctionto the source of 4.5<=A_J<=7.5 mag, and an infrared excess above ablackbody stellar continuum which is inherent to the source.
| The empirical scale of temperatures of the low main sequence (F0V-K5V).
We have calibrated the effective temperatures of the low main sequencestars ranging spectral types from F0 to K5 versus [Fe/H] and colours(B-V), (R-I), (V-R), (V-I), (V-K), (J-H), (J-K) and ubvy-β, using alarge sample of dwarfs and subdwarfs. The effective temperatures, scaledto direct T_eff_ determinations via reliable angular diametermeasurements, were derived applying the InfraRed Flux Method with thenew grid of atmosphere models developed by Kurucz (1993). We have fittedpolynomial functions of the form θ_eff_=P(colour,[Fe/H]) usingthe least squares method. The precision of the fits ranges from 30K for(V-K) to 154K for (J-H). The new relations have been compared toprevious calibrations. We also provide the empirical intrinsic colours(U-B), (B-V), (R-I), (V-R), (V-I), (V-K), (J-H), (J-K) and β, inthe ranges: 4000K[Fe/H]>-2.5.
| Determination of effective temperatures for an extended sample of dwarfs and subdwarfs (F0-K5).
We have applied the InfraRed Flux Method (IRFM) to a sample of 475dwarfs and subdwarfs in order to derive their effective temperatureswith a mean accuracy of about 1.5%. We have used the new homogeneousgrid of theoretical model atmosphere flux distributions developed byKurucz (1991, 1993) for the application of the IRFM. The atmosphericparameters of the stars cover, roughly, the ranges:3500K<=T_eff_<=8000K -3.5<=[Fe/H]<=+0.53.5<=log(g)<=5. The monocromatic infrared fluxes at the continuum,and the bolometric fluxes are derived using recent results, whichsatisfy the accuracy requeriments of the work. Photometric calibrationshave been revised and applied to estimate metallicities, although directspectroscopic determinations were preferred when available. The adoptedinfrared absolute flux calibration, based on direct optical measurementsof angular stellar diameters, sets the effective temperatures determinedusing the IRFM on the same scale than those obtained by direct methods.We derive three temperatures, T_J_, T_H_ and T_K_, for each star usingthe monochromatic fluxes at different infrared wavelengths in thephotometric bands J, H, and K. They show good consistency over 4000 K,and no trend with wavelength may be appreciated. We provide a detaileddescription of the steps followed for the application of the IRFM, aswell as the sources of the errors associated to the different inputs ofthe method, and their transmission into the final temperatures. We alsoprovide comparison with previous works.
| Optical, infrared and millimetre-wave properties of Vega-like systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.279..915S&db_key=AST
| Rest-frame optical line emission from the high-redshift galaxy 1614+051A
We report detections of [OIII] and H? emission from the radio-quietcompanion galaxy of the z=3.2 quasar PKS 1614+051. The Lyalpha/H?ratio for the galaxy is ~2+/-1, showing evidence for strong absorptionor scattering of the Lyalpha emission. The level of H? emissionfrom the companion is too high for it to result from gas photoionized byonly the quasar radiation, confirming that the gas in the galaxy isionized by an embedded source and that the companion galaxy is mildlyactive. The [OIII]/H? ratio in the object is lower than in nearbySeyfert 2 galaxies, which implies a low metallicity or a relatively lowionization state for the oxygen. If the latter is true, then carbonlines observed in the optical spectrum are at a higher ionization statethan the oxygen lines, further supporting the case for an embeddedsource of ionization in the galaxy, with a spectrum harder than that ofstarlight.
| CO and shocked H_2 in the highly collimated outflow from VLA 1623
We show large-scale ^12CO and H_2 images of the outflow from theproposed `class 0' young star VLA 1623. Shocked H_2 emission is clearlyassociated for the first time with this flow. Most of the H_2 lies incompact knots, each of which is downstream from a peak in thehigh-velocity CO. The total outflow mass derived from the CO data is0.10 M_solar, most of which lies in the extended blueshifted south-eastflow. The outflow in this direction is >=15 arcmin (0.7 pc) in lengthwith an opening angle of <=1.?6. It can be divided into tworegions: the first, within 0.07 pc of the star, has a conical shape.Beyond this radius, the low-velocity CO has a limb-brightenedmorphology, with a narrower, centrally peaked lane at high velocities;this is indicative of flow along the walls of a cylindrical cavity. Wesuggest that most expansion of the outflow cavity occurs within theinitial 0.07 pc of the source; beyond this, the molecular flow isconfined to a cylinder of constant width ~0.03 pc. Comparison of the COand H_2 results tends to suggest that the north-west side of VLA 1623may contain two separate flows. The near-infrared continuum image showsthe dense cloud around the VLA 1623 source in silhouette against abackground nebula. There is no evidence of elongation perpendicular tothe outflow direction, and the core has a sharp outer radius of ~0.02pc, with no evidence of a surrounding lower density accreting envelope.Fits to the radial distribution of extinction indicate a Gaussian ratherthan shallow power-law density gradient.
| Object 17: Another cluster of emission-line stars near the galactic center
Infrared imaging and spectroscopic studies suggest that regions ofrecent massive star formation exist in the center region of the Galaxy.Here, we present J(1.29 microns), H(1.67 microns), K(2.23 microns), andL'(3.82 microns) broadband images, as well as Br gamma and Br alphahydrogen recombination line images of the Object #17 detected in anear-infrared survey at a projected distance of 30 pc from the Galacticcenter. Our data show that this source is a cluster of luminous starswith emission lines. The line flux and width of these stars are similarto those of Of-type stars, Wolf-Rayet stars, and He I emission-linestars recently discovered in the central parsec of the Galaxy. However,although the He II line at 3.09 microns has been detected in Object #17,the He I line at 2.06 microns seems weak. The weakness contrasts withstars in the central parsec of the Galaxy. The broadband colors areconsistant with the idea that the #17 cluster is near tha Galacticcenter, and this consistancy is further evidence for the recentoccurrence of massive star formation near the Galactic center. It ispossible that this cluster is responsible for the ionization of thethermal arched filaments observed in the radio.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | へびつかい座 |
| Right ascension: | 17h48m19.22s |
| Declination: | -01°48'29.7" |
| Apparent magnitude: | 7.751 |
| Distance: | 99.8 parsecs |
| Proper motion RA: | 5.7 |
| Proper motion Dec: | 0.9 |
| B-T magnitude: | 8.083 |
| V-T magnitude: | 7.779 |
Catalogs and designations:
|
