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Dust Morphology and Composition in FU Orionis Systems
FU Orionis stars are a small group of pre-main-sequence stars known forlarge-amplitude optical variability. These objects also exhibitmultiwavelength phenomena suggestive of active accretion from acircumstellar disk. We present high spatial resolution mid-IR imagingand spectroscopy, submillimeter photometry, and 3-4 μm photometry offour FU Ori-class objects, RNO 1B and C, Z CMa, and Par 21, and oneobject classified as a pre-FU Ori star, V380 Ori. We resolve multiple IRsources and extended emission in the RNO 1B/C system, and we discuss indetail their association with disk activity and the source of theInfrared Astronomical Satellite far-IR and radio maser emission in thisfield. We derive dust temperatures and masses for all sources anddiscuss how dust composition and morphology is related to theevolutionary stage of these objects.
| Disk Evolution in the Orion OB1 Association
We analyze multiband photometry of a subsample of low-mass stars in theassociations Ori OB1a and 1b discovered during the Centro deInvestigaciones de Astronomía (CIDA) Orion Variability Survey,which have ages of 7-10 and 3-5 Myr, respectively. We obtainedUBVRCIC photometry at Mount Hopkins for sixclassical T Tauri stars (CTTSs) and 26 weak T Tauri stars (WTTSs) in OriOB1a and for 21 CTTSs and two WTTSs in Ori OB1b. We also obtained L-bandphotometry for 14 CTTSs at Mount Hopkins and 10 and 18 μm photometrywith OSCIR at Gemini for six CTTSs; of these, all six were detected at10 μm, whereas only one was detected at 18 μm. We estimate massaccretion rates from the excess luminosity at U and find that they areconsistent with determinations for a number of other associations, withor without high-mass star formation. The observed decrease of massaccretion rate with age is qualitatively consistent with predictions ofviscous evolution of accretion disks, although other factors can alsoplay a role in slowing accretion rates. We compare the excesses overphotospheric fluxes in H-K, K-L, and K-N with the younger sample ofTaurus and find an overall decrease of disk emission from Taurus to OriOB1b to Ori OB1a. This decrease implies that significant grain growthand settling toward the midplane has taken place in the inner disks ofOri OB1. We compare the spectral energy distribution of the stardetected at both 10 and 18 μm with disk models for similar stellarand accretion parameters. We find that the low fluxes shortward of 18μm of this Ori OB1b star cannot be due to the smaller disk radiusexpected from viscous evolution in the presence of the far-ultravioletradiation fields from the OB stars in the association. Instead, we findthat the disk of this star is essentially a flat disk, with little ifany flaring, indicating a significant degree of dust settling toward themidplane, as expected from dust evolution in protoplanetary disks.
| 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.
| The Identification of Infrared Synchrotron Radiation from Cassiopeia A
We report the discovery of polarized flux at 2.2 μm from the brightshell of the ~320 yr old supernova remnant Cas A. The fractionalpolarizations are comparable at 6 cm and 2.2 μm, and the polarizationangles are similar, demonstrating that synchrotron radiation from thesame relativistic plasma is being observed at these widely separatedwave bands. The relativistic electrons radiating at 2.2 μm have anenergy of ~150 GeV, (γ~3×105), assuming an ~500μG magnetic field. The total intensity at 2.2 μm lies close to thepower-law extrapolation from radio frequencies, showing thatrelativistic particle acceleration is likely an ongoing process; theinfrared emitting electrons were accelerated no longer than ~80 yr ago.There is a small but significant concave curvature to the spectrum, asexpected if the accelerating shocks have been modified by the backpressure of the cosmic rays; given calibration uncertainties, thisconclusion must be considered tentative at present. The 2.2 μmpolarization angles and the emission-line filaments observed by theHubble Space Telescope are both offset from the local radial directionby 10°-20°, providing evidence that the magnetic fields in Cas Aare generated by Rayleigh-Taylor instabilities in the deceleratingejecta.
| 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.
| Dust and molecules in the Local Group galaxy NGC 6822. III. The first-ranked HII region complex Hubble V
We present maps of the first-ranked HII region complex Hubble V in themetal-poor Local Group dwarf galaxy NGC 6822 in the first fourtransitions of 12CO, the 158 mu m transition ofC+, the 21-cm line of HI, the Pabeta line of HII, and thecontinuum at 21 cm and 2.2 mu m wavelengths. We have also determinedvarious integrated intensities, notably of HCO+ and near-IRH2 emission. Although the second-ranked HII region Hubble Xis located in a region of relatively strong HI emission, our mappingfailed to reveal any significant CO emission from it. The relativelysmall CO cloud complex associated with Hubble V is comparable in size tothe ionized HII region. The CO clouds are hot (Tkin = 150 K)and have high molecular gas densities (n( H2) ~104 cm-3). Molecular hydrogen probably extendswell beyond the CO boundaries. C+ column densities are morethan an order of magnitude higher than those of CO. The total mass ofthe complex is about 106 Msun and molecular gasaccounts for more than half of this. The complex is excited by luminousstars reddened or obscured at visual, but apparent at near-infraredwavelengths. The total embedded stellar mass may account for about 10%of the total mass, and the mass of ionized gas for half of that. HubbleV illustrates that modest star formation efficiencies may be associatedwith high CO destruction efficiencies in low-metallicity objects. Theanalysis of the Hubble V photon-dominated region (PDR) confirms in anindependent manner the high value of the CO-to- H2 conversionfactor X found earlier, characteristic of starforming low-metallicityregions.
| H II Emission from a Complete Spectroscopic Survey of Be Stars in h and χ Persei
We describe data for emission-line B stars observed in a spectroscopicsurvey of h and χ Persei. The survey is complete to V=12.5 andcovers an area of ~1100 arcmin2 roughly centered on the twoclusters. We detect 32 Be stars; some have low Hα emissionstrength. Seven of these are new identifications; seven others areconfirmations of Be stars previously identified using photometry. Fiveof the observed Be stars show significant Hα profile variationsfrom epoch to epoch. We show that spectral indices yield physicalcharacteristics of the H II emission region. This automatic method isrobust and easily applied to large spectroscopic samples. We inferHα:Hβ flux ratios of 2-5 and observe a linear relationshipbetween Hα emission and J-K color for these stars. We include aHertzsprung-Russell diagram for the B-type stars in the clusters.
| The Nature of Faint Companions to G-Type Stars from Adaptive Optics
High spatial resolution (0.30") near-IR photometric observations usingthe adaptive optics of the Mount Wilson 100 inch (2.5 m) telescope andthe Penn State IR Imager and Spectrograph have revealed faint companionsto HD 190067 and HIP 13855. HD 190067B is found to be of mass 0.075-0.1Msolar with an age from 0.5 Gyr to a few gigayears. HIP13855B is a low-mass star (age 100-500 Myr) of mass between 0.1 and 0.2Msolar. Further near-IR spectroscopic observations will benecessary to classify their spectral types precisely.
| 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.
| Near-Infrared Line Imaging of the Circumnuclear Starburst Ring in NGC 7771
We present high spatial resolution near-infrared broadband JHK imagesand, for the first time, Brγ 2.1661 μm and H2 1-0S(1) 2.122 μm emission-line images of the circumnuclear star-formingring (major axis diameter 7''=2 kpc) in the starburst galaxyNGC 7771. These data are used to investigate the morphology andextinction of the starburst ring and to study its star-formingproperties and history by comparing the observed quantities with anevolutionary population synthesis model. The clumpy morphology of NGC7771 varies strongly with wavelength, as a result of the combination ofextinction (for which we derive an average value of AV=2.8),emission from hot dust and red supergiants, and several stellargenerations in the ring. Also, the ellipticity and the position angle ofthe ring depend on the wavelength. The starburst ring in NGC 7771exhibits small Brγ equivalent widths. Assuming a constant starformation model with Mu=100 Msolar results in verylong lifetimes of the star-forming regions (up to 1 Gyr), indisagreement with the clumpy near-infrared morphology and the observedradio spectral index of NGC 7771. This situation is only slightlyremedied by assuming a reduced upper mass cutoff (Mu=30Msolar), resulting in ages between 8 and 180 Myr. We preferan instantaneous star formation model with Mu=100Msolar, which can explain the derived Brγ equivalentwidths if a single starburst occurred 6-7 Myr ago. The main excitationmechanism of the molecular gas, based on the observed S(1)/Brγratio, appears to be excitation by UV radiation from hot young stars. Wederive M~=1900 Msolar for the mass of the excitedH2.
| Thermal-infrared imaging of 3C radio galaxies at z~1
We present the results of a programme of thermal-infrared imaging of 19z ~ 1 radio galaxies from the 3CR and 3CRR (LRL) samples. We detectemission at L' (3.8 μm) from four objects; in each case the emissionis unresolved at 1-arcsec resolution. 15 radio galaxies remainundetected to sensitive limits of L' ~ 15.5. Using these data in tandemwith archived HST data and near-infrared spectroscopy, we show thatthree of the detected `radio galaxies' (3C 22, 3C 41 and 3C 65) harbourquasars reddened by A_V <~ 5 mag. Correcting for this reddening, 3C22 and 3C 41 are very similar to coeval 3C quasars, whilst 3C 65 seemsunusually underluminous. The fourth radio galaxy detection (3C 265) is amore highly obscured (A_V ~ 15) but otherwise typical quasar, whichpreviously has been evident only in scattered light. We determine thefraction of dust-reddened quasars at z ~ 1 to be 28_-13^+25 per cent at90 per cent confidence. On the assumption that the undetected radiogalaxies harbour quasars similar to those in 3C 22, 3C 41 and 3C 265 (asseems reasonable, given their similar narrow emission line luminosities)we deduce extinctions of A_V >~: 15 towards their nuclei. Thecontributions of reddened quasar nuclei to the total K-band light rangefrom ~0 per cent for the non-detections, through ~10 per cent for 3C 265to ~80 per cent for 3C 22 and 3C 41. Correcting for these effects doesnot remove the previously reported differences between the K magnitudesof 3C and 6C radio galaxies, so contamination by reddened quasar nucleiis not a serious problem for drawing cosmological conclusions from theK-z relation for radio galaxies. We discuss these results in the contextof the `receding torus' model which predicts a small fraction of lightlyreddened quasars in samples of high-radio-luminosity sources. We alsoexamine the likely future importance of thermal-infrared imaging in thestudy of distant powerful radio sources.
| 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.
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| Optical, infrared and radio observations of the Seyfert galaxy Markarian 315
We report on new optical, infrared and radio observations of the Seyfertgalaxy Markarian 315. We confirm the detection at all wavelengths of asecondary peak of emission, which lies ~2 arcsec east of the Seyfertnucleus. Moreover, we detect a chain-like structure which surrounds theactive nucleus, with peculiar behaviour westward of the nucleus. Weconsider different interpretations for the origin of the secondary peakemission.
| Near-Infrared Stellar Photometry of the M31 Spiral Arm around OB Association A24
Deep high-resolution JHK images of a 2' x 2' field around the OBassociation A24 near the 7 kpc spiral arm in M31 were measured to yieldphotometric data of more than 3000 stars with the faintest magnitudebeing J = 21.3, H = 20.5, and K = 19.6. The photometric data for the1037 stars that are brightest in the K band are presented. Judging fromthe color-magnitude and the two-color diagrams, we find that themajority of the observed stars are AGB stars including large-amplitudevariables. They are distributed smoothly over the observed field, and wefind no clear evidence of varying extinction over the field for thesered stars. The present sample includes bright AGB stars of M_K <= -8and about 30 young blue objects of (J-H) < 0.75 that are brighterthan M_J ~= -6.5.
| 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
| High spatial resolution `shift-and-add' imaging at UKIRT: multiplicity amongst young stellar objects
We present results from near-infrared `shift-and-add' imaging at UKIRTusing the upgraded near-infrared imaging camera, IRCAM3, and new controlelectronics, ALICE. Commissioning data on 12 sources in the Ophiuchusdark cloud complex are described. All but one source have previouslybeen studied using 2D speckle imaging. We compare the results obtainedby the two techniques and demonstrate that `shift-and-add' imaging withIRCAM3 can produce results comparable to those obtained by the 2Dspeckle technique. We additionally discuss both the current imagingquality of UKIRT and its predicted performance after the plannedthermal, dynamical and optical upgrades.
| Near-Infrared Imaging Polarimetry of Embedded Young Stars in the Taurus-Auriga Molecular Cloud
We describe near-infrared (JHK) imaging polarimetry of 21 embeddedprotostars in the Taurus-Auriga molecular cloud. These objects displayextended, highly polarized reflection nebulae with V-shaped, unipolar,and bipolar morphologies. Most sources have PK ~ 5%-20% in an 8"aperture; a few objects have PK <~ 5%. The polarization increasestoward shorter wavelengths and is generally aligned perpendicular to thelong axis of the reflection nebula. We develop an analytic scatteringmodel for the near-IR colors and polarizations of embedded protostars.Our Taurus data require visual extinctions, AV ~ 25-60 mag, comparableto those predicted for models of collapsing clouds. The ratio ofscattered flux to intrinsic source flux ranges from Fs/F0 ~ 0.001 at1.25 mu m to Fs/F0 ~ 0.015 at 3.5 mu m. These results indicate that theobserved ratio of scattered light to direct (extincted) light increasesfrom Fs/Fd ~ 0.1 at 3.5 mu m to Fs/Fd ~ 25 at 1.25 mu m. Our datafurther require intrinsic colors of 0.6 <~ J-H <~ 0.9, 0.3 <~H-K <~ 0.6, and 0.4 <~ K-L <~ 1.2 for the central sources ofTaurus protostars. We adopt the Terebey, Shu, & Cassen solution foran infalling, rotating protostellar cloud and use a two dimensionalMonte Carlo radiative transfer code to model the near-IR polarizationdata for this sample. Our results indicate envelope parameters inagreement with previous estimates from broadband spectral energydistributions and near-IR images. We estimate infall rates, M dot~(2-5)x10^{-6} Mȯ yr-1; centrifugal radii, Rc ~ 10-50 AU; andopening angles of the bipolar cavity, theta h ~ 10 deg-20 deg, for atypical object. Standard grain parameters can explain the near-IR colorsand polarizations of Taurus protostars. The polarization maps show thatTaurus grains have a high maximum polarization at K, Pmax,K >~ 80%.The large image sizes of this sample further imply a high K-band albedo,omega K ~ 0.3-0.4. Model polarization maps indicate that the size of the"polarization disk" increases with the size of the instrumentalpoint-spread function. Relating the morphology of polarization vectorsto disk or envelope properties thus requires some care and a goodunderstanding of the characteristics of the instrument.
| Molecular hydrogen morphology, kinematics and excitation in AFGL 2688 and NGC 7027.
We report the first results of spectro-imaging post-AGB objects in thenear-infrared K'-band using a new instrument called BEAR. Thisinstrument has been used to obtain high spatial (0.6") and spectral(~40km/s) resolution observations of the proto-planetary nebula AFGL2688 and the young planetary nebula NGC 7027. The current paper isdevoted to a detailed study of the morphology, velocity field, andexcitation of H_2_ in their circumstellar envelopes. In AFGL 2688, theH_2_ emission shows four bright clumps forming a remarkable cross-likepattern with weaker H_2_ emission connecting the north and east, and thesouth and west clumps, respectively. No trace of lines or continuum fromionized gas is seen in the spectra. The continuum emission seen in thecentral parts of the nebula is stellar light scattered by nebular dust.The velocity field shows that the northern and eastern clumps areblue-shifted whereas the southern and western clumps are red-shiftedwith respect to the systemic velocity. There is also evidence forsignificant velocity gradients across the H_2_ structures. The emissionof the H_2_ lines in AFGL 2688 is consistent with shock excitation. InNGC 7027 new morphological details are revealed by the observations. Theemission from the inner envelope is dominated by continuum and lineemission from the ionized nebula, including strong Brγ, HeII andHeI lines. The H_2_ emission is distributed at the periphery of theionized gas, along a four-lobed clover pattern with an equatorial toruswhich is seen for the first time in its entirety. The H_2_ velocitydistribution demonstrates that the kinematics of the hot gas traced byH_2_ is firmly linked to the outer molecular envelope. The H_2_ emissionin NGC 7027 is consistent with excitation in the UV photon dominatedregion (PDR) at the interface of the ionized and molecular gas. Themorphology and excitation of H_2_ in AFGL 2688 and NGC 7027 areconsistent with an evolutionary scheme in which fast winds during theproto-planetary nebula phase develop strong shocks in the slowerexpanding AGB envelope and are able to excite the H_2_ emission, and inthe young planetary nebula phase ultraviolet radiation from the hot,central star ionizes the inner cavity and excites the molecular hydrogenin the PDR.
| 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.
| Photometry of the intermediate-age open cluster NGC 2141
Optical V and I, and a selection of near-infrared J and H observationsare presented for the open cluster NGC 2141. The colour excess E(B-V)has been determined as 0.35+/-0.07 mag, based on the positions ofseveral giants and clump stars in a (V-I, J-H) diagram. The distancemodulus (m-M)_V is found to be 14.16+/-0.16 (4.2+/-0.4 kpc), based on acomparison between the magnitudes of the red giant clump stars in NGC2141 and M67. The age is estimated to be 2.5 Gyr, from a comparison ofthe colour-magnitude diagram with convective overshooting isochrones fora metallicity of Z=0.006.
| The Nuclear Energy Sources Powering Bright Infrared-selected Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...447..545A&db_key=AST
| A Near-Infrared Reflection Nebula Associated with NGC 2024 FIR 4
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...440..722M&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| A K' imaging survey of molecular outflow sources
A K'-band imaging survey with a approximately equals 8 min x 3 min fieldof view of all regions associated with CO molecular outflow from thelist of Fukui (1989) has been conducted. We present the individualimages and describe individual nebulous objects and star clusters. Thedata, including photometric calibration data, are being published asFITS files on a CD-ROM. The vast majority of all outflow sources areassociated with nebulosity detectable in K', so such nebulae can be usedas tracers for very young stars. We find a significant fraction(one-third) of molecular outflow sources to be associated with clustersof young stars. Most of the young embedded clusters show peaks in theirK' magnitude histograms that, if interpreted as an evolutionary effect,indicate average ages of the embedded star population of is less than 1x 106 yr.
| The lowest mass stars in the Hyades
In Bryja et al. (1992), we presented proper motions and photometry of 12very low mass star and brown dwarf candidates in the Hyades cluster,selected on the basis of colors and proper motions measured from threeepochs of plate material. We here present new observations of some ofthese candidates, including seven low resolution spectra, plus motionsand photometry of 17 fainter additional candidates. Most of thecandidates have JHK colors typical of M5-M8 dwarfs, while their opticalcolors are consistent with earlier M spectral types. The availablespectra consist of late M dwarfs with H alpha emission featuresindicative of Hyades membership, earlier M dwarf background stars, andtwo anomalous objects with early M dwarf features but unusually redcontinua. We find that the proper motion distribution of faint red fieldstars in the region is irregular, and it is not possible to determine ifthe anomalous objects are Hyades members or background field stars. Inthe most conservative view, only five of our 29 candidates are Hyades.These five stars have optical and infrared colors consistent with thebottom of the Hyades main sequence, with four of them also shown to havelate M dwarf spectra. It follows that these are the lowest mass starsknown in the Hyades (M is about 0.1 solar mass).
| Sensitive imaging polarimetry of the faint infrared reflection nebula in B5 IRS1
The paper presents sensitive polarimetric images at J, H, and K of thefaint reflection nebulosity in the low-mass young stellar object B5IRS1. Multiepoch photometry, compared with existing data, shows that thenear-IR luminosity of B5 IRS1 has varied significantly between 1983 and1990, declining steadily in near-IR brightness while maintainingvirtually constant near-IR colors. This may suggest an increase ofneutral extinction by grains which are growing in a circumstellar disk,which is speculated to have later accreted into planetesimals. Thenebula is composed of light scattered in a thin, limb-brightened dustshell partly surrounding the blueshifted lobe of the molecular outflowfrom IRS1. An estimate of the density in the scattering dust shellindicates rough pressure equilibrium between the shell and the molecularflow, and a sound-crossing time in the shell close to the dynamical ageof the flow.
| Infrared imaging of the compact H II region W3A
The H II region W3A was imaged and mapped at five broad-band wavelengthsfrom 1.65 to 20 microns and at CVF resolution in the Br-gamma line at2.17 microns and in the nearby continuum. A newly discovered sourcecalled IRS 2c appears to be a highly reddened star similar to IRS 2. IRS11 is another previously undetected source that lies between W3A and W3IRS 5. The 1-20 micron spectrum of IRS 11 is due to warm dust and has amoderate silicate absorption at 9.7 microns. The most interesting sourcefirst shown on the maps, called IRS 2b, appears to be a reddened starsurrounded by a centrally condensed cloud of hot dust. It is suggestedthat IRS 2b is a young star in a dust-clearing phase. The maps alsoreveal that the dust-to-gas emission ratio appears to be variable withinW3A.
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