共查询到20条相似文献，搜索用时 46 毫秒
1.
The near-infrared variable source, IRAS 04000+5052, was observed using the Italian 1.5 m TIRGO infrared telescope, located in the Gornergrat Observatory, Switzerland. High-resolution images were obtained in the JHK broad bands and H2 S(1) 1-0, Brγ narrow bands. Photometry and astrometry were also carried out. From the observations, it is found that IRAS source is not a single young object, but a small-sized, compact star-forming region with many young objects. Even in such a small and compact region, stars are not formed at the same time. 相似文献
2.
A.J. Burston M.J. Ward R.I. Davies 《Monthly notices of the Royal Astronomical Society》2001,326(1):403-415
We present near-infrared observations of a sample of mainly interacting ultraluminous infrared galaxies, comprising H - and K -band spectra. Our main aims are to investigate the power source of these extremely luminous objects and the various excitation mechanisms of the strong molecular hydrogen emission often seen in such objects. Broadened emission lines were only detected in one object, IRAS 23498, consistent with the previous results for this galaxy. The [Si vi ] emission line was detected in IRAS 17179 and 20210, both classified as Sy2s. Two of the samples were unclassified, IRAS 00150 and 23420, which exhibit neither [Si vi ] emission nor broadened H i emission. However this does not rule out the presence of an obscured AGN. Analysis of the molecular hydrogen emission showed that the major excitation mechanism for most objects was thermal. Modelling of the more luminous objects indicates that for IRAS 20210 10 per cent, and for both IRAS 23365 and IRAS 23420 30 per cent, of the 1–0 S(1) line emission has a non-thermal origin. 相似文献
3.
Spectroscopic observations by the 2.6 m BAO telescope of IRAS galaxies identified on the basis of the First Byurakan Survey (BIG objects) are reported. Slit spectra were obtained for 16 objects, including components of 7 multiple systems and 2 individual galaxies. The red shifts were measured, and the radial velocities, distances, absolute stellar magnitudes, and infrared and far infrared luminosities were calculated. A diagnostic diagram has been constructed based on the intensity ratios of emission lines and the activity types of the objects have been determined. Two LINERs, five galaxies with composite spectra (Comp, one of which has Sy2 features) and seven HII regions were found. Two objects are ultraluminous IR galaxies (ULIG). It is shown that all the multiple systems are physical pairs or groups. The observed high IR luminosity confirms the view that ULIG/HLIGs may be associated with interactions of galaxies. 相似文献
4.
Albedos for 57 asteroids were determined using diameters obtained from stellar occultations. For 18 objects, the occultation albedos were determined to accuracies better than 5%. The effect on the occultation albedo due to errors in the asteroid absolute magnitude is discussed and correlations between the occultation albedos and IRAS and polarimetric albedos are presented. The higher-quality occultation albedos presented here are suitable for calibrating albedos obtained by indirect methods. 相似文献
5.
The near-Earth object (99942) Apophis will make an extremely close approach to the Earth in 2029, and currently has approximately a one-in-45,000 chance of impacting our planet in 2036 (JPL Sentry, November 2006). Computation of the orbital evolution of this object is limited by insufficient knowledge of physical properties required to determine the role played by non-gravitational effects. Using polarimetric observations, we have obtained the first reliable determination of the albedo of Apophis, obtaining 0.33±0.08. We also derive an updated estimate of the asteroid's absolute magnitude: H=19.7±0.4. Using this albedo and H, we find that Apophis has a diameter of 270±60 m, slightly smaller than preliminary estimates based upon an assumed albedo. Our observations demonstrate the feasibility of polarimetric observations aimed at obtaining albedos and sizes of small, potentially hazardous asteroids. 相似文献
6.
We present the results of a campaign of polarimetric observations of small asteroids belonging to the Karin and Koronis families, carried out at the ESO Cerro Paranal Observatory using the VLT-Kueyen 8-m telescope. The Karin family is known to be very young, having likely been produced by the disruption of an original member of the Koronis family less than 6 Myr ago. The purpose of our study was to derive polarimetric properties for a reasonable sample of objects belonging to the two families, in order to look for possible systematic differences between them, to be interpreted in terms of differences in surface properties, in particular albedo. In turn, systematic albedo differences might be caused by different times of exposure to space weathering processes experienced by the two groups of objects. The results of our analysis indicate that no appreciable difference exists between the polarimetric properties of Karin and Koronis members. We thus find that space-weathering mechanisms may be very efficient in affecting surface properties of S-class asteroids on very short timescales. This result complements some independent evidence found by recent spectroscopic studies of very young families. 相似文献
7.
Results of the first polarimetric observations of Centaurs (5145) Pholus and (10199) Chariklo, and new observations of (2060) Chiron are presented together with the estimates of their absolute magnitudes. Observations were carried out at the 8 m ESO Very Large Telescope in 2007-2008. They revealed noticeable negative polarization in the phase-angle range 0.5-4.4° with a minimum varying from −1% to −2.1% in the R band. All three objects show diverse polarization phase-angle behaviour, each distinctly different from that of transneptunian objects. We found evidence of surface heterogeneity for Chariklo while Chiron and Pholus appear to have rather homogeneous surfaces. Polarization phase behaviours of Chiron and Pholus are significantly different from any other Solar System bodies studied so far. A shift of negative polarization minima toward small phase angles seems to be a characteristic feature of polarization properties of Centaurs. Presence of a small amount of water frost on a dark surface is considered as one of the possible ways to explain these properties. 相似文献
8.
A sample of 230 galaxies has been compiled based on their IRAS FSC fluxes to study their multiwavelength properties and carry
out comparative analyses with other similar samples. To understand the nature of these galaxies, a comparison with a sample
of bright ULIRGs having fluxes at 60 μm fν > 1 Jy and 14 optically faint IRAS FSC galaxies is presented. This comparison shows that galaxies found by IRAS are not always
strong infrared sources and that the objects from the sample of ULIRGs represent a sample of extreme galaxies, which are very
powerful infrared sources. We have confirmed the consistency between Star Formation Rates (SFRs) calibrated based on luminosities
of the PAH feature at 7.7 μm and radio 1.4 GHz flux densities. We have estimated the extinction for our 230 objects using
SFRs calibrated from the PAH feature compared to ultraviolet flux, which shows that only 1% of the ultraviolet continuum typically
escapes extinction by dust within a starburst. 相似文献
9.
A.D. Karnik S.K. Ghosh T.N. Rengarajan R.P. Verma 《Monthly notices of the Royal Astronomical Society》2001,326(1):293-302
High-resolution far-infrared observations of a large area of the star-forming complex RCW 106 obtained using the TIFR 1-m balloon-borne telescope are presented. Intensity maps have been obtained simultaneously in two bands centred around 150 and 210 μm. Intensity maps have also been obtained in the four IRAS bands using HIRES-processed IRAS data. From the 150- and 210-μm maps, reliable maps of dust temperature and optical depth have been generated. The star formation in this complex has occurred in five linear sub-clumps. Using the map at 210 μm, which has a spatial resolution superior to that of IRAS at 100 μm, 23 sources have been identified. The spectral energy distribution (SED) and luminosity of these sources have been determined using the associations with the IRAS maps. The luminosity distribution of these sources has been obtained. Assuming these embedded sources to be zero-age main-sequence stars and using the mass–luminosity relation for these, the power-law slope of the initial mass function is found to be −1.73±0.5 . This index for this very young complex is about the same as that for more evolved complexes and clusters. Radiation transfer calculations in spherically symmetric geometry have been undertaken to fit the SEDs of 13 sources with fluxes in both the TIFR and the IRAS bands. From this, the r −2 density distribution in the envelopes is ruled out. Finally, a correlation is seen between the luminosity of embedded sources and the computed dust masses of the envelopes. 相似文献
10.
A star formation region connected with SNO 41 is investigated. The observations of this region were carried out in the 12CO (1-0) line and in the 1.2-mm (with SIMBA) with the 15-m SEST mm telescope (Cerro La Silla, Chile). A blue shifted outflow
is revealed from the 12CO(1-0) observations, while a bipolar outflow is apparent from the 1.2-mm SIMBA image. In CO it seems that a very faint dust
envelope around SNO 41 probably exists, which is expanding with a velocity of ∼10.5 km/s. The distance to SNO 41 is estimated
as ∼1500 pc. There are outflows also present in 2MASS images. A spiral jet has a condensation (resembling a HH object) at
the end. Another jet has a discontinuity and a bow-shock-like structure on it. In 2MASS images there are also spots resembling
HH objects. In this region there is also a rather luminous point source (IRAS 08546-4254), which has IR colors typical for
an YSO connected with a water maser. The detection of a strong CS (2-1) line emission toward IRAS 08546-4254, with the same
velocity as the CO line, shows the existence of a high density core of molecular gas associated to this source. A methanol
maser is also associated with that IRAS source. The existence of CS line emission and a methanol maser (at 6.669 Ghz) is an
indication of the presence of a very young massive star. It is not excluded that this IRAS source is the center of outflows
mentioned above, because this source coincides with the center of the 1.2-mm SIMBA image and also with the place of origin
of the jet with bow-shock-like structure.
Published in Astrofizika, Vol. 50, No. 1, pp. 5–15 (February 2007). 相似文献
11.
Observations of the submillimeter polarized dust emission is an important tool to study the role of the magnetic fields in the evolutions of molecular clouds and in the star formation processes. The Submillimeter Array (SMA) is the first imaging submillimeter interferometer. The installation of quarter wave plates in front of the 345 GHz receivers has allowed to carry out polarimetric observations. We present high angular resolution 345 GHz SMA observations of polarized dust emission towards the low-mass protostellar system NGC 1333 IRAS 4A. We show that in this system the observed magnetic field morphology is in agreement with the standard theoretical models of formation of low-mass stars in magnetized molecular clouds at scales of a few hundred AU; gravity has overcome magnetic support and the magnetic field traces a clear hourglass shape. The magnetic field is substantially more important than turbulence in the evolution of the system and the initial misalignment of the magnetic and spin axes may have been important in the formation of the binary system. 相似文献
12.
The sample of Byurakan–IRAS galaxies (BIG) has been created based on optical identifications of IRAS Point Source Catalog (PSC) at high galactic latitudes. As a result, 1178 galaxies have been identified. 172 of them have been observed spectroscopically with Byurakan Astrophysical Observatory (BAO, Armenia) 2.6 m, Special Astrophysical Observatory (SAO, Russia) 6m and Observatoire de Haute Provence (OHP, France) 1.93 m telescopes. Later on, spectra were obtained for more 83 BIG objects in Sloan Digital Sky Survey (SDSS). We have extracted and studied these spectra, classified them and measured spectral features. Diagnostic diagrams have been built to distinguish starbursts (SB), LINERs and Seyfert galaxies. Cross-correlations weremade for these objects with multiwavelength (MW) catalogues and their physical properties were studied. Among these 83 objects, 55 HII, 8 Seyfert galaxies, 2 LINERs, 4 other AGN, 6 composite spectrum objects, and 8 other emission-line galaxies have been revealed. Three of these objects are Ultra-Luminous InfraRed Galaxies (ULIRG). 相似文献
13.
Results of spectral observations of 45 objects from the BIG sample (corresponding to 35 IRAS sources) obtained on the 2.6-m
telescope at the BAO are reported. Emission lines are observed for 42 galaxies, 1 object is an absorption galaxy, and 2 turned
out to be stars. The red shifts are determined, the radial velocities, distances, sizes, and absolute stellar magnitudes are
calculated, the parameters of the spectral lines are determined, the objects are classified according to their activity type,
and the IR and far IR luminosities are calculated. Of the 42 emission galaxies, 1 was type Sy2, 2 were LINERs, 1 was an AGN
(Sy2 or LINER), 4 were composite, 25 were HII (including 6 with nuclear star-formation activity), and 9 were Em of undetermined
type (3 of which may be AGN). Calculations show that 23 of the objects are LIG. A physical coupling is discovered for 9 multiple
systems. Spectra of some of the galaxies are shown.
__________
Translated from Astrofizika, Vol. 49, No. 1, pp. 23–40 (February 2006). 相似文献
14.
A. L. Gyulbudaghian 《Astrophysics》1998,41(4):382-391
The relationship of stellar associations, IRAS point sources, and water masers with two types of objects, which were discovered
primarily at Byurakan, is investigated. They are cometary nebulae and Herbig-Haro (H-H) objects. It is shown that almost all
of these objects are affiliated with OB or T associations. Two groupings of nonsteady objects have been found. They may belong
to unknown T associations. About half of the cometary nebulae and H-H objects were found to be affiliated with IRAS point
sources; 22% of the H-H objects and 8% of the cometary nebulae are associated with water masers.
Translated from Astrofizika, Vol. 41. No. 4, pp. 585–598, October–December, 1998. 相似文献
15.
Wil van Breugel 《Astrophysics and Space Science》1999,266(1-2):23-28
Radio continuum emission at cm wavelengths is relatively little affectedby extinction. When combined with far-infrared (FIR) surveys thisprovides for a convenient and unbiased method to select (radio-loud)AGN and starbursts deeply embedded in gas and dust–rich galaxies. Suchradio-selected FIR samples are useful for detailed investigations ofthe complex relationships between (radio) galaxy and starburst activity, and to determine whether ULIRGs are powered by hidden quasars (monsters) or young stars (babies).We present the results of a large program to obtain identifications andspectra of radio-selected, optically faint IRAS/FSC objects using theFIRST/VLA 20 cm survey (Becker, White and Helfand 1995). These objects are all radio-`quiet' in the sense that their radiopower / FIR luminosities follow the well-known radio/FIR relationshipfor star forming galaxies.We compare these results to a previous study by our group of a sampleof radio-`loud' IRAS/FSC ULIRGs selected from the Texas 365 MHzsurvey (Douglas etal. 1996). Many of these objects alsoshow evidence for dominant, A-type stellar populations, as well as highionization lines usually associated with AGN. These radio-loud ULIRGshave properties intermediate between those of starbursts and quasars,suggesting a possible evolutionary connection.Deep Keck spectroscopic observations of three ULIRGs from these samplesare presented, including high signal-to-noise spectropolarimetry.The polarimetry observations failed to show evidence of a hidden quasar inpolarized (scattered) light in the two systems in which the stellar lightwas dominated by A-type stars. Although observations of a larger samplewould be needed to allow a general conclusion, our current data suggestthat a large fraction of ULIRGs may be powered by luminous starbursts,not by hidden, luminous AGN (quasars). 相似文献
16.
A fourth list of point sources from the IRAS Point Source Catalog (PSC) that are optically identified with stars of late spectral
types is given. The list contains data on 41 objects. The identifications were based on the Digital Sky Survey (DSS), the
First Byurakan Survey, blue and red maps of the Palomar Observatory Sky Survey, and infrared fluxes at the wavelengths 12,
25, 60, and 100 μm in the region of +65° ≤ δ ≤ +69° and 05h10m ≤ α ≤ 18h10m. Of the 41 objects, which are given in the IRAS PSC as unidentified sources of infrared emission, 9 are associated with known
stars in existing catalogs while 32 sources remained unidentified in the optical range, one of which is also a source in the
deep IRAS survey (IRAS Serendipitous Source Catalog). The optical coordinates, their departures from the IR coordinates, the
V stellar magnitudes, the color indices CI, and the preliminary spectral subtypes have been determined. The objects have optical
magnitudes in the range of 8m.5-14m.5. Finder charts from the DSS are given for 32 of the objects.
Translated from Astrofizika, Vol. 43, No. 3, pp. 361-368, July–September, 2000. 相似文献
17.
The results of V-band polarimetric observations of the potentially hazardous near-Earth Asteroid (23187) 2000 PN9 at large phase angles are presented as well as its photometric observations in BVRI bands. Observations were made in March-April 2006 during its close approach to the Earth using the 1.82-m Asiago telescope (Italy) and the 0.7-m telescope at the Chuguevskaya Observational Station (Ukraine). We obtained polarimetric measurements at the phase angle of 115°, the largest phase angle ever observed in asteroid polarimetry. Our data show that the maximum value of the polarization phase curve reached 7.7% and occurred in the phase angle range of 90-115°. The measured values of linear polarization degree, BVRI colors and magnitude-phase dependence correspond to the S-type composition of this asteroid. Based on our observations the following characteristics of the Asteroid (23187) 2000 PN9 were obtained: a rotation period of 2.5325±0.0004 h, a lightcurve amplitude of 0.13 mag, an albedo of 0.24±0.06 and a diameter of 1.6±0.3 km. 相似文献
18.
H. Boehnhardt G. P. Tozzi M. Sterzik S. Bagnulo L. Kolokolova K. Muinonen 《Earth, Moon, and Planets》2009,105(2-4):95-100
We present a brief review of polarimetric measurements of solar system objects, both linear and circular, obtained with the FORS1 instrument at the Very Large Telescope VLT over the past years. A number of first and new results have been obtained by using this unique observing mode at an 8 m class telescope, among them polarimetry of faint planetary bodies like near-Earth asteroids, Kuiper Belt objects and cometary nuclei, spectropolarimetry of cometary coma material and of the Earthshine of the Moon (in order to verify that life exists on Earth!). We outline the science cases for planetary polarimetry at a future Extremely Large Telescope ELT and provide high level requirements for polarimetric equipment to be used at the ELTs for the study of the science cases described. 相似文献
19.
Th. Boller 《Astrophysics and Space Science》1999,266(1-2):49-54
A sample of 323 Ultraluminous IRAS galaxies (ULIRGs) has been correlatedwith the ROSAT All-Sky Survey and ROSAT public pointed observations.22 objects are detected in ROSAT survey observations, and 6 ULIRGs aredetected in addition in ROSAT public pointed observations. The detection is basedon a visual inspection of the X-ray contour maps overlaid on optical imagesof ULIRGs taken from the Digitized Sky Survey.Simple power law fits were used to compute the absorption-correctedfluxes of the ROSAT detected ULIRGs. The ratio of the soft X-ray flux to thefar-infrared luminosity is used to estimate the contributionfrom starburst and AGN emitting processes. These results are comparedwith the ISO SWS ULIRG diagnostic diagram. 相似文献
20.
V. H. Chavushyan O. V. Verkhodanov J. R. Valdés R. Mújica S. A. Trushkin 《Astrophysics》2005,48(1):89-98
A list of 750 objects has been compiled using the Astrophysical CATalogs Support System (CATS) database, by cross-identifying sources in the IRAS catalogues and the catalogue of the Texas survey at 365 MHz. We have carried out a search for optical counterparts of those objects, where the difference in positions between the two catalogues and the APM is less than 3. One of these sources, IRAS F02044+0957, was observed with the RATAN-600 radio telescope at four frequencies in April 1999. Optical spectroscopy of the components of the system was made with the 2.1-m telescope of the Guillermo Haro Observatory. The radio and optical spectra, the NVSS radio map and the optical and infrared images allow us to conclude that the steep spectrum (=–0-94 ± 0-02) radio source IRAS F02044+0957 is a pair of interacting galaxies, a LINER and a HII galaxy, at z=0.093.Published in Astrofizika, Vol. 48, No. 1, pp. 113–124 (February 2005). 相似文献