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NGC 3503



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A Compact Array imaging survey of southern bright-rimmed clouds
We have carried out a radio-wavelength imaging survey of 45bright-rimmed clouds (BRCs), using the Australia Telescope Compact Arrayto characterise the physical properties in their ionised boundarylayers. We detected radio emission from a total of 25 clouds and using acombination of Digitised Sky Survey and mid-infrared MSX 8 \mum imagesclassified the emission into that associated with the ionised cloudrims, that associated with embedded possible massive YSOs and thatunlikely to be associated with the clouds at all. A total of 18 cloudsdisplay radio emission clearly associated with the cloud rim and wedetermine the ionising photon flux illuminating these clouds and theelectron density and pressure of their ionised boundary layers. Using aglobal estimate for the interior molecular pressure of these clouds weshow that the majority are likely to be in pressure equilibrium andhence are currently being shocked by photoionisation-induced shocks. Weidentify those clouds where the predicted ionising photon flux isinconsistent with that derived from the observations and show thateither the spectral types of the stars illuminating the BRCs are earlierthan previously thought or that there must be additional ionisingsources within the HII regions. Finally, we identify the radio sourcesembedded within the clouds with infrared stellar clusters and show thatthey contain late O and early B-type stars, demonstrating that a numberof BRCs are intimately involved with high to intermediate-mass starformation.Full Figs. \ref{fig:images} and \ref{fig:sfo86dss} are only available inelectronic form at http://www.edpsciences.org

New infrared star clusters in the southern Milky Way with 2MASS
We carried out a 2MASS J, H and Ks survey of infrared starclusters in the Milky Way sector 230deg< l <350deg. This zone was the least studied in the literature,previously including only 12 infrared clusters or stellar groups with|b|< 10deg, according to the recent catalogue by Bica etal. (2003). We concentrated efforts on embedded clusters, which arethose expected in the areas of known radio and optical nebulae. Thepresent study provides 179 new infrared clusters and stellar groups,which are interesting targets for detailed future infrared studies. Thesample of catalogued infrared clusters and stellar groups in the Galaxyis now increased by 63%.

Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141

Internal Variation of Electron Density in Galactic and Extragalactic HII Regions
Not Available

Reddening and age for 13 southern Galactic open clusters determined from integrated spectra
In this study we present flux-calibrated integrated spectra in the range3800-6800 Å for 13 concentrated open clusters with Galacticlongitudes between 219deg and 316deg, nine ofwhich have not been previously studied. Using the equivalent widths ofthe Balmer lines and comparing the cluster spectra with template spectraof Magellanic Clouds and Galactic star clusters with known parameters,we derive both foreground interstellar reddening values and age. Fornine clusters these two parameters have been determined for the firsttime, while for the rest of the sample the results show good agreementwith previous studies. The present analysis indicates four very young(Hogg 11, NGC 5606, vdB-RN 80 and Pismis 17), seven moderately young(ESO 429-SC13, Hogg 3, Hogg 12, Haffner 7, BH 87, NGC 2368 and Bochum12) and two intermediate-age (Berkeley 75 and NGC 2635) open clusters.The derived foreground interstellar reddening values are in the range0.00 <= E(B-V) <= 0.38. The age and reddening distributions of thepresent sample of relatively faint open clusters match those of openclusters with known parameters in a 90deg sector centered atl = 270deg. Based on observations made at ComplejoAstronómico El Leoncito, which is operated under agreementbetween the Consejo Nacional de Investigaciones Científicas yTécnicas de la República Argentina and the NationalUniversities of La Plata, Córdoba and San Juan, Argentina.

Integrated photometry of galactic H Ii regions
Integrated photoelectric measurements of the equivalent width W_Hβ, the [O Iii]/Hβ ratio and the Hβ emission line flux arepresented for 31 southern hemisphere galactic H Ii regions. The Lymancontinuum photon fluxes are obtained for some of these objects. Theintegrated [O Iii]/Hβ ratios have not shown any statisticallysignificant deviation from non-integrated measurements found in theliterature.

Internal variation of electron density in galactic Hbt II regions
A study on the internal variation of the electron density in galactic HIi regions has been conducted on a sample of 15 objects of differentsizes and evolutionary stages. The [S Ii] lambda 6716/lambda 6731 lineratio was adopted as electron density indicator. Long slitspectrophotometry of high signal-to-noise ratio with spectral dispersionof 0.75 Ä,pxl-1 and spatial scale of 0\farcs90pxl-1 were obtained at different slit positions andorientations. No systematic spatial variation of electron density wasdetected in nearly half of the objects studied (S255, S 257, S 271,S 285, S 301, S305, NGC 3372 and IC1275). They are in general the most diffuse and probablyevolved objects with low mean densities in the range Ne ~20-140 cm-3. The remaining objects (S 288,S 307, NGC 2579, NGC3503, Gum 62, Gum 64aand M 20) with mean densities Ne ~ 80-360cm-3, have shown a statistically significant electron densitydependence on position. In most of these cases, the spatial variation ofdensity may be interpreted as a radial gradient with the densitydecreasing from the centre to the edges. M 20 shows asystematic non-radial variation of electron density with maximum valuesoccurring at its prominent dark lanes. A mean filling factor of theorder of phi = 0.1 was found compatible with the data. Based on theirdensity profiles, NGC 2579, Gum62, Gum 64a and possibly NGC3503 were indicated as candidates of showing a `champagneflow'.

Molecular Clouds and Star Formation in the Southern H II Regions
We have carried out extensive 13CO(J = 1-0) observationstoward 23 southern H II regions associated with bright-rimmed clouds. Intotal, 95 molecular clouds have been identified to be associated withthe H II regions. Among the 95, 57 clouds \ are found to be associatedwith 204 IRAS point sources which are candidates for young stellarobjects. There is a significant increase of star-formation efficiency onthe side facing to the H II regions; the luminosity-to-mass ratio,defined as the ratio of the stellar luminosity to the molecular cloudmass, is higher by an order of magnitude on the near side of the H II \regions than that on the far side. This indicates that molecular gasfacing to the H II regions is more actively forming massive s\ tarswhose luminosity is >~ 103 LO . In addition, the numberdensity of the IRAS point sources increases by a factor of 2 on the nearside of the H II regions compared with on the far side. These resultsstrongly suggest that the active formation of massive stars on the nearside of the H II regions is due to the effects of the H II regions, suchas the compression of molecular material by the ionization/shock fronts.For the whole Galaxy, we estimate that the present star-formation rateunder such effects is at least 0.2-0.4 MO yr-1, correspondingto a few 10% by mass.

Searches for Bright-Rimmed Clouds with IRAS Point Sources
Not Available

A catalog of bright-rimmed clouds with IRAS point sources: Candidates for star formation by radiation-driven implosion. 2: The southern hemisphere
Forty-five bright-rimmed clouds associated with Infrared AstronomicalSatellite (IRAS) point sources have been selected in the southernhemisphere from the ESO (R) Atlas in addition to the 44 objects of thenorthern work (Pape I). Again they are good candidates for the sites ofstar formation induced by radiation-driven implosion. Four of them areknown to be associated with HH objects, and three with molecularoutflows. Most of their sizes are approximately less than 1 pc, and theluminosities of the associated IRAS sources, approximately 20 to 3 x104 solar luminosity, are much larger than those of the IRASsources associated with Bok globules or dense cores in dark cloudcomplexes, both having a similar mass range. This suggests thatintermediate-mass stars or multiple-star systems are mainly formed inbright-rimmed clouds. IRAS luminosity to cloud mass ratios aresignificantly greater than those in Bok globules or dense cores. Theresults confirm most of the findings of Paper I.

Catalogue of southern stars embedded in nebulosity.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..208V&db_key=AST

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Observation and Astrometry data

Right ascension:11h01m30.00s
Apparent magnitude:99.9

Catalogs and designations:
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NGC 2000.0NGC 3503

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