Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
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.
| Optical and infrared observations of the TypeIIP SN2002hh from days 3 to 397
We present optical and infrared (IR) observations of the TypeII SN2002hhfrom 3 to 397d after explosion. The optical spectroscopic (4-397d) andphotometric (3-278d) data are complemented by spectroscopic (137-381d)and photometric (137-314d) data acquired at IR wavelengths. This is thefirst time L-band spectra have ever been successfully obtained for asupernova (SN) at a distance beyond the Local Group. The VRI lightcurves in the first 40d reveal SN2002hh to be an SNIIP (plateau) - themost common of all core-collapse SNe. SN2002hh is one of the most highlyextinguished SNe ever investigated. To provide a match between itsearly-time spectrum and a coeval spectrum of the TypeIIP SN1999em, aswell as maintaining consistency with KI interstellar absorption, weinvoke a two-component extinction model. One component is due to thecombined effect of the interstellar medium (ISM) of our Milky Way Galaxyand the SN host galaxy, while the other component is due to a `dustpocket' where the grains have a mean size smaller than in the ISM. Theearly-time optical light curves of SNe1999em and 2002hh are generallywell matched, as are the radioactive tails of these two SNe and SN1987A.The late-time similarity of the SN2002hh optical light curves to thoseof SN1987A, together with measurements of the optical/IR luminosity and[FeII]1.257μm emission indicate that 0.07 +/- 0.02Msolarof 56Ni was ejected by SN2002hh. However, during the nebularphase the HKL' luminosities of SN2002hh exhibit a growing excess withrespect to those of SN1987A. We attribute much of this excess to anIR-echo from a pre-existing, dusty circumstellar medium. Based on anIR-echo interpretation of the near-IR (NIR) excess, we deduce that theprogenitor of SN2002hh underwent recent mass-loss of~0.3Msolar. A detailed comparison of the late-time opticaland NIR spectra of SNe1987A and 2002hh is presented. While the overallimpression is one of similarity between the spectra of the two events,there are notable differences. The MgI1.503μm luminosity of SN2002hhis a factor of 2.5 greater than in SN1987A at similar epochs, yet coevalsilicon and calcium lines in SN2002hh are fainter. Interpreting thesedifferences as being due to abundance variations, the overall abundancetrend between SN1987A and 2002hh is not consistent with explosion modelpredictions. It appears that during the burning to intermediate-masselements, the nucleosynthesis did not progress as far as might have beenexpected given the mass of iron ejected. Evidence for mixing in theejecta is presented. Pronounced blueshifts seen in the more isolatedlines are attributed to asymmetry in the ejecta. However, during thetime-span of these observations (~1-yr post-explosion) we find noevidence of dust condensation in the ejecta such as might have beenrevealed by an increasing blueshift and/or attenuation of the red wingsof the emission lines. Nevertheless, the clear detection of firstovertone CO emission by 200d and the reddening trend in (K -L')0 suggest that dust formation in the ejecta may occur atlater epochs. From the [OI] λλ6300, 6364Å doubletluminosity we infer a 16-18Msolar main-sequence progenitorstar. The progenitor of SN2002hh was probably a red supergiant with asubstantial, dusty wind.
| A giant molecular cloud falling through the heart of Cygnus A: clues to the triggering of the activity
We present intermediate-resolution near-infrared long-slit spectroscopicdata for the nearby radio galaxy Cygnus A (3C 405) (obtained with theNIRSPEC spectrograph on the Keck II telescope). The data revealconsiderable complexity in the near-infrared emission-line kinematics,including line splittings of 200-350 km s-1 and a mixture ofnarrow (FWHM ~ 200 km s-1) and broad (FWHM ~ 700 kms-1) components to the emission lines. It is notable that thePaα and H2 emission lines show markedly differentkinematics, both on- and off-nucleus. Overall, the data provide evidencefor the presence of a giant molecular cloud falling through the heart ofthe Cygnus A host galaxy, the motion of which is not driven by theactive galactic nucleus itself. We suggest that this cloud may beconnected to the triggering of the activity in this highly powerfulactive galactic nucleus. We also detect split H2 componentson the nucleus that are likely to originate in the circumnuclear torus.
| Circumnuclear Shock and Starburst in NGC 6240: Near-Infrared Imaging and Spectroscopy with Adaptive Optics
We have obtained adaptive optics, high spatial resolution (0.15"),K-band spectra and images of the region around the two active nuclei inNGC 6240, which show the presence of circumnuclear shocks. The data areconsistent with thermal excitation being the dominant mechanism in thenuclear region. UV fluorescence and associative detachment may alsocontribute to the fraction of energy emitted through molecular hydrogentransitions. The near-IR continuum emission appears closely associatedwith the two active nuclei. The morphological similarities between thenear-IR images and the Chandra X-ray images indicate that the samemechanisms may be responsible for the emission in the near-IR and X-raybands.
| 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.
| Molecular Outflows in the Young Open Cluster IC 348
We present a wide-field survey of the young open cluster IC 348 formolecular H2 outflows. Outflow activity is only found at itssouthwestern limit, where a new subcluster of embedded sources is in anearly phase of its formation. If the IC 348 cluster had been built up bysuch subclusters forming at different times, this could explain thelarge age-spread that Herbig (1998) found for the IC 348 member stars.In addition to several compact groups of H2 knots, our surveyreveals a large north-south oriented outflow, and we identify the newlydiscovered far-infrared and millimeter object IC 348 MMS as its source.New deep images in the 1-0 S(1) line of molecular hydrogen trace the HH211 jet and counterjet as highly collimated chains of knots, resemblingthe interferometric CO and SiO jets. This jet system appears rotatedcounterclockwise by about 3° with respect to the prominentH2 bow shocks. Furthermore, we resolve HH 211-mm as a doublepointlike source in the millimeter continuum.Based on observations taken at the German-Spanish Astronomical Centre,Calar Alto, operated by the Max-Planck-Institute für Astronomie,Heidelberg, jointly with the Spanish National Commission for Astronomyand on observations with ISO, an ESA project with instruments funded byESA Member States (especially the PI countries: France, Germany, theNetherlands, and the United Kingdom) and with the participation of ISASand NASA.
| Spectroscopy of the near-nuclear regions of Cygnus A: estimating the mass of the supermassive black hole
We use a combination of high spatial resolution optical andnear-infrared spectroscopic data to make a detailed study of thekinematics of the narrow-line region (NLR) gas in the near-nuclearregions of the powerful, FRII radio galaxy Cygnus A (z= 0.0560), withthe overall goal of placing limits on the mass of any supermassive blackhole in the core. Our K-band infrared observations (0.75-arcsec seeing)- taken with NIRSPEC on the Keck II telescope - show a smooth rotationpattern across the nucleus in the Paα and H2 emissionlines along a slit position (PA180°) close to perpendicular to theradio axis, however, there is no evidence for such rotation along theradio axis (PA105°). Higher spatial resolution observations of the[OIII]λ5007 emission line - taken with STIS on the Hubble SpaceTelescope (HST) - confirm the general rotation pattern of the gas in thedirection perpendicular to the radio axis, and provide evidence forsteep velocity gradients within a radius of 0.1 arcsec of the core -corresponding to the high surface brightness structure visible inhigh-resolution narrow-band images. The [OIII] line remains broadthroughout the core region (FWHM ~ 300-900 km s-1), but thespatial distribution of [OIII] provides no evidence for an unresolvedinner narrow-line region (INLR). Assuming that the ionized gas iscircularly rotating in a thin disc and that the large linewidths are dueto activity-induced turbulence, the circular velocities measured fromboth the Keck and HST data lead to an estimate of the mass of thesupermassive black hole of 2.5 +/- 0.7 × 109Msolar. For the host galaxy properties of Cygnus A, this massis consistent with the global correlations between black hole mass andhost galaxy properties deduced for non-active galaxies. Therefore,despite the extreme power of its radio source and the quasar-likeluminosity of its active galactic nucleus (AGN), the black hole inCygnus A is not unusually massive considering the luminosity of its hostgalaxy. Indeed, the estimated mass of the black hole in Cygnus A issimilar to that inferred for the supermassive black hole in the FRIradio galaxy M87, despite the fact that the AGN and radio jets of CygnusA are two to three orders of magnitude more powerful. Overall, theseresults are consistent with the idea that the properties and powers ofthe AGN in radio galaxies are determined as much by the mass accretionrates as by the absolute masses of their supermassive black holes.As well as providing evidence for a supermassive black hole in the coreof Cygnus A, our data also demonstrate that nuclear activity has animportant effect on the kinematics of the circumnuclear gas on asubkiloparsec scale. Most notably, the velocity offsets measured in thetwo outer HST/STIS slit positions are consistent with the presence of anactivity-induced outflow in the NW cone.
| 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.
| 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.
| Large-Scale Extended Emission around the Helix Nebula: Dust, Molecules, Atoms, and Ions
We present new observations of the ionized gas, molecular gas, and cooldust in the Helix Nebula (NGC 7293). The ionized gas is observed in theform of an Hα image, which is constructed using images from theSouthern Hα Sky Survey Atlas. The molecular emission was mappedusing the H2 v=1-->0 S(1) line at 2.122 μm. Thefar-infrared (FIR) observations were obtained using ISOPHOT on theInfrared Space Observatory. The Hα observations are more sensitivethan previous measurements and show the huge extent of the Helix,confirming it as a density-bounded nebula and showing previously unseenpoint-symmetric structures. The H2 observations show that themolecular gas follows the distribution of molecular material shown inprevious work. The molecular emission is confined to that part of thenebula seen in the classic optical image. Furthermore, comparison of theH2 emission strength with time-dependent models forphotodissociation regions (PDRs) shows that the emission arises fromthermal excitation of the hydrogen molecules in PDRs and not fromshocks. The FIR observations, at 90 and 160 μm, represent mostlycontributions from thermal dust emission from cool dust grains butinclude a small contribution from ionized atomic lines. Comparison ofthe FIR emission with the Hα observation shows that the dust andionized gas are coincident and extend to ~1100" radius. This equates toa spatial radial extent of more than 1 pc (assuming a distance to theHelix of ~200 pc). Assuming that the outer layers of the circumstellarshell have spherical symmetry, radiative transfer modeling of theemission in Hα gives a shell mass of ~1.5 Msolar.However, the modeling does not cover the outermost part of the shell(beyond ~600" radius), and therefore this is a lower limit for the shellmass. Moreover, the models suggest the need for very large dust grains,with ~80% of the dust mass in grains larger than 3.5 μm. Comparisonof these new observations with previous observations shows thelarge-scale stratification of the Helix in terms of ionized gas anddust, as well as the coexistence of molecular species inside the ionizedzones, where molecules survive in dense condensations and cometaryknots.
| Molecular Gas in NGC 7129
This paper reports new submillimeter molecular line observations of NGC7129, a reflection nebula and star-forming region. Maps of12CO and 13CO 2-1 and 3-2 emission show a cavitysurrounded by bright ridges of denser molecular gas. Known molecularoutflows in the region issue from deeply embedded sources in theseridges. Only the red lobe of the most prominent outflow is seen clearly,but there is some evidence to suggest that a blue counterjet is escapingthrough the front of the cavity. We suggest a picture of the region'sevolution in which the oldest star, BD +65°1638, created the cavityby sweeping the surrounding interstellar gas into the surroundingridges. This led to further star formation, as evidenced by the outflowsources found in the ridges. One of these sources, FIRS 2, thought to bean intermediate-mass analog of a Class 0 young stellar object, iscoincident with a pointlike source seen in a near-IR (K') image.
| Multiple H2 protostellar jets in the bright-rimmed globule IC 1396-N
We present near infrared images of the bright rimmed globule IC 1396-Nin the H_2 2.12 mu m narrow band filter as well as in broad band J, H,and K, filters. We detected several chains of collimated H_2 knotsinside the globule, having different luminosities but similarorientations in the sky. Most of the knots are associated with peaks ofhigh velocity CO emission, indicating that they trace shocked regionsalong collimated stellar jets. From the H2 knots morphologyand orientation, we identify at least three different jets: one of themis driven by the young protostar associated with IRAS 21391+5802, whichrepresents the most luminous object in the region, while we were able toidentify only one of the two other driving sources by means of nearinfrared photometry. Our photometry reveals the existence of a clusterof young embedded sources located in a south-north line which followsthe distribution of the high density gas and testifies for a highlyefficient star formation activity through all the globule. Based onobservations collected with the AZT-24 Telescope at Campo Imperatore, ajoint project between the Astronomical Observatories of Roma (OAR,Italy), Teramo (OACT, Italy) and Pulkovo (OAP, Russia).
| Near-Infrared Spectroscopy of the Compact H II Region W51 IRS 2
Medium-resolution (R~460) spectra in the K window have been obtained forthe compact H II regions W51 IRS 2 East and IRS 2 West. Brγ, He I,three lines of [Fe III], and seven lines of molecular hydrogen(H2) have been detected. The unidentified line at 2.288 μmwas also detected with ~2% of the intensity of Brγ. We derive anelectron density of ~105-106 cm-3 inboth IRS 2 East and IRS 2 West from [Fe III] line ratios. In bothregions, observed H2 line ratios indicate that the excitationof H2 is dominated by fluorescence rather than by shocks.
| Infrared L-Band Observations of the Trapezium Cluster: A Census of Circumstellar Disks and Candidate Protostars
We report the results of a sensitive near-infrared JHKL imaging surveyof the Trapezium cluster in Orion. We use the JHKL colors to obtain acensus of infrared excess stars in the cluster. Of (391) stars brighterthan 12th magnitude in the K and L bands, 80%+/-7% are found to exhibitdetectable infrared excess on the J-H, K-L color-color diagram.Examination of a subsample of 285 of these stars with published spectraltypes yields a slightly higher infrared excess fraction of 85%. We findthat 97% of the optical proplyds in the cluster exhibit excess in theJHKL color-color diagram indicating that the most likely origin of theobserved infrared excesses is from circumstellar disks. We interpretthese results to indicate that the fraction of stars in the cluster withcircumstellar disks is between 80%-85%, confirming earlier publishedsuggestions of a high disk fraction for this young cluster. Moreover, wefind that the probability of finding an infrared excess around a star isindependent of stellar mass over essentially the entire range of thestellar mass function down to the hydrogen burning limit. Consequently,the vast majority of stars in the Trapezium cluster appear to have beenborn with circumstellar disks and the potential to subsequently formplanetary systems, despite formation within the environment of a richand dense stellar cluster. We identify 78 stars in our samplecharacterized by K-L colors suggestive of deeply embedded objects. Thespatial distribution of these objects differs from that of the rest ofthe cluster members and is similar to that of the dense molecular cloudridge behind the cluster. About half of these objects are detected inthe short wavelength (J and H) bands, and these are found to becharacterized by extreme infrared excess. This suggests that many ofthese sources could be protostellar in nature. If even a modest fraction(i.e., ~50%) of these objects are protostars, then star formation couldbe continuing in the molecular ridge at a rate comparable to that whichproduced the foreground Trapezium cluster.
| Red Quasars and Quasar Evolution: The Case of BAL QSO FIRST J155633.8+351758
We present the first near-infrared spectroscopic observations of theradio-loud broad absorption line quasi-stellar object (QSO), FIRSTJ155633.8+351758. The spectrum is similar to that of a reddened QSO andshows strong emission lines of Hα and Hβ, as well as strongFe II emission blends near Hβ. The redshift of the object, measuredfrom the Hα and Hβ lines, is zBLR=1.5008+/-0.0007,slightly larger than the redshift of zmetal=1.48, estimatedfrom the broad metal absorption features. Thus, the broad metalabsorption features are blue shifted with respect to the systemicvelocity. The width of the Hα emission line (FWHM~4100 km s-1) is typical of that observed in QSO broad-line regions, but theBalmer decrement (Hα/Hβ~5.8) is larger than that of mostoptically selected QSOs. Both the Balmer decrement and the slope of therest-frame UV-optical continuum independently suggest a modest amount ofextinction along the line of sight to the broad-line region(EB-V~0.5 for SMC-type screen extinction at the redshift ofthe QSO). The implied gas column density along the line of sight is muchless than that implied by the weak X-ray flux of the object, suggestingthat either the broad emission and absorption line regions have a lowdust-to-gas ratio or that the rest-frame optical light encounterssignificantly lower mean column density lines of sight than the X-rayemission. From the rest-frame UV-optical spectrum, we are able toconstrain the stellar mass content of the system(<3×1011 Msolar). Comparing this masslimit with the black hole mass estimated from the bolometric luminosityof the QSO, we find it possible that the ratio of the black hole tostellar mass is comparable to the Magorrian value, which would implythat the Magorrian relation is already in place at z=1.5. However,multiple factors favor a much larger black hole-to-stellar mass ratio.This would imply that if the Magorrian relation characterizes the latehistory of QSOs and if the situation observed for F1556+3517 is typicalof the early evolutionary history of QSOs, central black hole massesdevelop more rapidly than bulge masses. Based on observations at theKitt Peak National Observatory.
| [Fe II] Bubbles in the Young Planetary Nebula Hubble 12
We have obtained narrowband images of the young planetary nebula Hubble12 showing [Fe II] line emission in bipolar bubbles near the core.Bright [Fe II] emission is strong evidence for shocks, suggesting thepresence of a high-velocity wind emanating from the central star. Wecompare our data to previously published images of Hubble 12-findingsimilar structures in hydrogen recombination and free-free emission-andwe propose three possible interpretations of the data: that the bubblesindicate the inner shock of the fast wind, that the [Fe II] emission isevidence of the outer shock of an episodic wind, or that the emission iscooling line radiation from a photodissociation region. We argue thatthe first two interpretations are more likely, since the [Fe II]emission must be shock excited.
| A near infrared study of the HII/photodissociation region DR 18 in Cygnus
Near infrared observations of DR 18, a HII region in the Cygnus Xmolecular complex, are presented in this paper. These observationsreveal DR 18 as an arc-shaped nebula in the 2.2 mu m region, with acentral star of V=15.6 obscured by A_V =~ 8 magnitudes. Visible andnear-infrared spectroscopy and photometry indicate a spectral typearound B0.5V for this star, while a near-infrared color-color diagram ofthe stars in the area shows that the central star is the most luminousone of a loose aggregate. Analysis of the narrow band imaging in the Kband suggests that the arc nebulosity is principally due to emission bysmall grains, heated by the central star, in a photodissociation region.We interpret the arc nebula as the interface between a molecular cloudthat is being eroded by the central star and the resulting HII region.Using published models of photodissociation regions, we estimate thedensity in the arc nebula to be a few times 10(3) cm(-3) . We brieflydiscuss the possible relation of the structures observed in the nearinfrared with the source IRAS 20333+4102, which has been included inseveral far infrared and radio studies of the area. We conclude thatIRAS 20333+4102 is not directly related to any of the structures that wedescribe here, and could be an intermediate mass protostar embeddeddeeper in the molecular cloud. The emission associated to ionized gas inDR 18 has a morphology fairly different from that of the arc nebula,being brighter near the position of the central star. A crescent-shapedpeak is observed beside the central star and facing the arc nebula,suggesting an interaction between a stream of ionized gas from thenebula and the wind from the central star. We present two dimensionalgas dynamical simulations which successfully reproduce such gas stream,the bow shock ahead of the central star, and the overall appearance ofthe nebula. An essential component of our model is the existence of anoutward-decreasing density stratification in the cloud being eroded, asis commonly observed in dense molecular clumps. The simple geometry ofthe nebula and the observability of the central star at shortwavelengths make the derivation of the physical conditions of the regionand the modeling of its dynamical evolution comparatively easier than inother, similar regions. DR 18 thus provides a good case study of severalfeatures associated to the interaction of an early B star with amolecular cloud. Based on observations collected at the German-SpanishAstronomical Center (Calar Alto, Spain), and at the European SouthernObservatory (La Silla, Chile)
| 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.
| 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
| The ultracompact H II region G45.45+0.06. A pearl necklace in the sky
We present new imaging data on the ultracompact H ii region G45.45+0.06at near- and mid-infrared wavelengths. High-resolution data were takenin the H and K' bands using ESO's adaptive optics system ADONIS. Theresulting images with a generic resolution of 0.4″ for the firsttime allow the resolution of the object into several single point-likesources. Additionally, we present images obtained in the mid-infrared at3.5, 10, and 12 mu m. A Br>~mma image was obtained to serve as ameasure for the extinction towards this region. We derive the physicalproperties of the point sources and show that some of them are young,massive stars. By combining our data with earlier VLA maps, we measurethe extinction towards the region and discuss the history of the object.Finally, we conclude that G45.45+0.06 is a young OB cluster similar tothe KL/BN Region in Orion and that sequential star formation is thereason for its present morphology. Based on observations collected atthe European Southern Observatory, La Silla, Chile. Prop. ID:55.C-0647.Based on observations collected at the DSAZ astronomical centre on CalarAlto, Spain
| Time-resolved Photometry and Spectroscopy of the Cataclysmic Variable V592 Cassiopeiae
Over the past 10 years, the cataclysmic variable (CV) V592 Cassiopeiae(LS I 55 deg-8) has been monitored by one of the authors. We now presenttime-resolved optical and infrared photometry and optical spectroscopyof this nova-like binary. Analysis of these data provides the firstorbital solution for this star. We find an orbital period near 0.114days (2.7 hr), a system inclination of 28 deg, and a mass ratio(M_2/M_1) of 0.19. V592 Cas appears to be a nova-like cataclysmicvariable with a massive white dwarf primary and lies inside the CVperiod gap.
| Characteristics of the 2MASS Prototype Survey
The 2 Micron All Sky Survey (2MASS) will catalog over 100,000,000individual objects, the vast majority of which will be stars of spectraltype K and later. For many projects it will be important to developtechniques to identify interesting objects within this data set. Thecombination of near-IR and visible light observations will be a powerfultool for finding objects from brown dwarfs to dust-enshrouded quasars.This paper describes prototype hardware and software systems used aspart of the preparation for the 2MASS survey. Three years ofobservations with prototype systems have produced a database of morethan 1 million objects. A companion paper describes the comparison ofthese data with optical plate material and visible spectroscopicobservations resulting in the discovery of a quasar with a redshift of0.147.
| The remarkable asymmetric outflow from the Cygnus EGG Nebula
We present ground based continuum images in the infrared, from 1.2 to19mu m, and an H_2 2.122mu m line emission image of the post-AGB starAFGL2688, the Cygnus Egg Nebula. We show that the standard model of thissource, comprising a fast wind focussed by a dense, equatorial, dustytorus into a bipolar flow at position angle 15(deg) and close to theplane of the sky, cannot explain the combination of kinematicinformation from previous studies and morphological information in ourown observations. Nor are the images consistent with a classical bipolarflow, since the apex of the two lobes observed in scattered light in thevisible and near-IR are offset in R.A. with respect to one another. Wesuggest a model which is physically similar, but substantially differentgeometrically, in which there is a bipolar flow at a position anglecloser to 60(deg) , rather than 15(deg) , still collimated by a dense,equatorial, dusty torus, but the opening angle of the cones out of whichthe fast bipolar flow is directed is closer to 90(deg) , rather than20(deg) or so as previously suggested. The bipolar flow axis is inclinedby about 20--30(deg) , rather than in the plane of the sky as inprevious models. The dust distribution in the nebula has to be extremelyclumpy, and there is evidence that large scale mass loss from theprogenitor AGB star occurred in discrete phases, recurring on atimescale of ~ 750 years. This model implies a much lower velocity forthe `fast' bipolar outflow than does the standard model, which isconsistent with very recent Nobeyama Millimetre Array images in (13) COemission. In support of our new model, we present a full radiativetransfer model for the source, in axial symmetry, which reveals that thefinal phase of heavy mass loss included a superwind phase which lastedabout two hundred years and removed about 0.7 Msun from theenvelope of the progenitor AGB star. Our results imply that theprogenitor star must have been a relatively high mass AGB star. Ourradiative transfer model also demonstrates convincingly that, incontrast with previous models, the core of the nebula has to beexceptionally optically thick, with an optical depth greater than unityeven at 10mu m.
| 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.
| A Multiresolution Infrared Imaging Study of LkH alpha 198
New near-infrared images of the young, nebulous, intermediate-mass(Herbig Ae/Be) star LkH alpha 198 using direct imaging, adaptive-opticscompensated speckle imaging, and standard speckle imaging reveal complexstructure in its circumstellar dust distribution. At high resolution,LkH alpha 198 is found to possess a barlike feature which extends ~3"from the star in either direction. Geometrical considerations suggestthat the bar is unlikely to represent light scattered by either astandard circumstellar disk, a disequilibrium "pseudodisk," or anambient halo illuminated by starlight escaping along the polar axis of adisk. Its orientation suggests that it may be associated with thefan-shaped nebula that surrounds LkH alpha 198. The infrared companion6" north of the star is found to be significantly extended atnear-infrared wavelengths and may be an example of a deeply embeddedobject with an envelope that is at least partially illuminated from theoutside.
| Near-Infrared Photometric And Polarimetric Observations Of Comet Hale-Bopp
Near-infrared photometric and polarimetric observations of cometHale-Bopp (1995 O1) using KONIC (Kiso Observatory Near-Infrared Camera)are reported. Observations were carried out on March 18 UT and April 26UT 1997, when the heliocentric distances of the comet were 0.94 and 1.02AU, and the phase angles were 48.5 deg and 32.9 deg, respectively. Inthe J, H, and K′ bands, we obtained linear polarization of thenear-nucleus region of 16.4 ± 1.2, 18.8 ± 1.3, and 15.1± 0.9 percent on March 18UT and 7.1 ± 1.1, 8.9 ±1.0, and 6.9 ± 0.6 percent on April 26, respectively. Thesevalues were higher than those observed for 1P/Halley. The maximumpolarization was found at H band on both dates. Polarization maps showedhigher polarization regions toward the anti-solar direction in the J andH bands. No distinct correlation was found between high polarizationregions and bright regions. The projected expansion velocity of the arcstructure of the dust jet was 375 ± 35.7 m/s on 17 19 March. Theperiodicity was found to be 11.1 ± 2.8 hours.
| Near-Infrared Spectroscopy of Molecular Filaments in the Reflection Nebula NGC 7023
We present near-infrared spectroscopy of fluorescent molecular hydrogen(H2) emission from molecular filaments in the reflection nebula NGC7023. We derive the relative column densities of H2rotational-vibrational states from the measured line emission andcompare these results with several model photodissociation regionscovering a range of densities, incident UV fields, and excitationmechanisms. Our best-fit models for one filament suggest, but do notrequire, either a combination of different densities, suggesting clumpsof 106 cm-3 in a 104--105 cm-3 filament, or a combination of fluorescentexcitation and thermally excited gas, perhaps due to a shock from abipolar outflow. We derive densities and UV fields for these molecularfilaments that are in agreement with previous determinations.
| Multiwavelength Observations of Collisional Ring Galaxies.I.Broad-Band Images, Global Properties, and Radial Colors of the Sample Galaxies
This is one of a series of papers discussing the optical, infrared andradio continuum properties of a sample of collisional ring galaxies. Thepresent paper concentrates on the global broad-band optical (B, V and R)and near-IR (J, H and K) images of the galaxies and describe theirglobal properties. An analysis of the colors of the galaxies over avariety of wavelength baselines is described. In the B and V bands, thebluest colors are found in the outer bright ring. The B-V colors of thesample of galaxies are blue, the median value for the sample is B-V =0.60, and V-K= 2.33 mag. The IR morphology of the galaxies is, in mostcases, very similar to that of the B-band data, suggesting that theclumpy appearance of the star formation in the outer rings is real, andnot a result of patchy dust obscuration. Only in one ring (WN1, aSeyfert ring galaxy) was the IR morphology different from the optical,suggesting the presence of significant dust in the disk. In II Hz 4,faint spiral arms are seen within the ring. There is a suggestion thatthe larger rings have redder V-K colors, which may be due to anincreased incidence of nuclear bulges in larger ring galaxies. Radialprofiles of surface brightness and color are presented for fourgalaxies. In all cases, the colors becomes bluer as one proceedsradially outwards, but in two galaxies, the rings redden again outsidethe main ring, suggesting the existence of a red stellar population thatmay have pre-dated the collisions.
| Photometry of the post-common-envelope binary PG 0308+096
We present R- and H-band photometry of PG 0308+096. We demonstrate thatthe orbital modulation is consistent with that of a dwarf M star heatedby a DA white dwarf within the constraints given by the kinematicparameters. By fitting the photometry with an irradiation model wedetermine that the radius of the white dwarf is 0.019<=R_wd<=0.026R_ (90 per cent confidence). In order to derive these limits, we havedeveloped a fitting procedure that takes account of the externalconstraints derived from the spectroscopic analysis by Saffer et al. Wedetermine that the period of the system is 0.286654+/-0.00000078d, whichis one of the cycle count aliases considered by Saffer et al. We showthat the Hα emission from the surface of the red star can bemodelled as either optically thick or thin, but in the latter case thered dwarf must have intrinsic emission.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Hattyú |
| Rektaszcenzió: | 21h23m35.53s |
| Deklináció: | +40°01'07.0" |
| Vizuális fényesség: | 7.209 |
| Távolság: | 138.122 parszek |
| RA sajátmozgás: | 29.6 |
| Dec sajátmozgás: | 7.6 |
| B-T magnitude: | 7.372 |
| V-T magnitude: | 7.223 |
Katalógusok és elnevezések:
|
INHABITED SKY
