AKARI Infrared Imaging of Reflection Nebulae IC4954 and IC4955 (original) (raw)
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An infrared-submillimeter study of starforming regions selected by the ISOSS 170 μm survey
Astronomy and Astrophysics, 2008
Context. Using the ISOPHOT Serendipity Survey (ISOSS) at 170 µm a sample of galactic star-forming regions exhibiting very cold dust temperatures (< 20 K) and high masses (> 100 M ⊙) has been established. Aims. We characterise the star-forming content of five regions that were selected as potential sites for early stage high-mass star formation. Methods. We use SCUBA (JCMT) observations in the submillimeter to identify the dense condensations of cold gas and dust. Sensitive mid-to far-infared Spitzer observations with IRAC and MIPS allow us to detect associated young stellar objects. From the long-wavelength emission we derive dust temperatures and masses for the identified clumps. A sample of associated mid-infrared sources is investigated using infrared color-color diagrams and the comparison to a model SED grid to constrain their evolutionary stages and derive estimates for additional parameters like the central mass. Results. In every region we identify between one and four submillimeter clumps with projected sizes between 0.1 and 0.4 pc. The dust temperatures range from 11.6 to 21.3 K and the estimated clump masses are 2 to 166 M ⊙. Towards the majority of submillimeter peaks we find point sources in the near-to mid-infrared. Most are interpreted as low-mass young stellar objects but we also detect very red sources. They probably represent very young and deeply embedded protostars that continue to accrete clump material and may reach higher masses. Several candidate intermediate-mass proto-or pre-main-sequence stars embedded in the clumps are identified. Conclusions. A subset of four clumps may be massive enough (> 100 M ⊙) to form high-mass stars and accompanying clusters. The absence of stellar precursors with current masses in the high-mass regime leave the type of star formation occuring in the clumps unsettled. We confirm the presence of large fractions of cold material as derived from large-scale far-infrared measurements which dominates the emission of most clumps and suggests that the star-forming process will continue.
Sub-Arcsec Resolution Infrared Images of the Star Forming Region G 35.20-1.74
1997
We present J(1.25 μm), H(1.65 μm), K(2.2 μm), H2(2.125 μm) and 11.2μm infrared images at sub-arcsec resolution of an area centered around the star forming region G 35.20-1.74. In J, H and K a cluster of early type stellar sources with infrared excess clearly stands out with respect to the background distribution and is associated with a diffuse K emission around an UC HII region (which is the brightest source at K). No H2 emission is detected in narrow-band images at 2.125μm. At 11.2μm six components are detected. The brightest one (MIR3) is extended and coincides with the UC HII region. The source with steepest IR spectrum and the largest infrared excess (MIR1) is associated with an H2O maser and a near IR source detected only at K. It is separated from the IR cluster and at a distance of 20′′ from the UC HII region. The IR emission comes from a local young stellar object (YSO) associated with the maser. The lack of radio continuum emission from MIR1 confirms that H2O masers can tr...
An infrared study of the high-mass, multistage star-forming region IRAS 12272−6240
Monthly Notices of the Royal Astronomical Society, 2020
IRAS 12272−6240 is a complex star-forming region with a compact massive dense clump (DC) and several associated masers, located at a well-determined distance of d = 9.3 kpc from the Sun. For this study, we obtained sub-arcsec broad- and narrow-band near-infrared (near-IR) imaging and low-resolution spectroscopy with the Baade/Magellan telescope and its camera PANIC. Mosaics of size 2 × 2 arcmin2 in the JHKs bands and with narrow-band filters centred in the 2.12 μm H2 and 2.17 μm Br γ lines were analysed in combination with Hi-GAL/Herschel and archive IRAC/Spitzer and WISE observations. We found that the compact DC houses two Class I young stellar objects (YSOs) that probably form a 21000 -au-wide binary system. Its combined 1–1200 μm spectral energy distribution is consistent with an O9V central star with a 10−2,mathrmModot10^{-2} \, \mathrm{M}_\odot10−2,mathrmModot disc and a 1.3times104,mathrmModot1.3 \times 10^4 \, \mathrm{M}_\odot1.3times104,mathrmModot dust envelope. Its total luminosity is 8.5times104,mathrmLodot8.5 \times 10^4 \, \mathrm{L}_\odot8.5times104,mathrmLodot. A series of shocked H...
Near-infrared study of southern massive star formation regions
Astronomy and Astrophysics, 2007
Context. We present the results of a near-infrared survey of the young stellar cluster associated with the IRAS 16571-4029 source. Aims. The main purpose of this survey is to study the cluster members and find the ionizing sources of the associated HII region. Methods. The stellar population was studied by using color-color and color-magnitude diagrams, as well as by analysing the spectral energy distributions in the near-and mid-infrared wavelengths. The extended emission was studied by the construction of contour diagrams, which were compared with near-and mid-infrared images. We computed the corresponding number of Lyman continuum photons (using the integrated Brγ flux density) and compared it with that obtained from the 5 GHz flux density to derive a mean visual extinction. Results. NIR observations in the direction of RCW116B reveal the presence of a young cluster of massive stars coincident with the IRAS 16571-4029 source. These observations, together with published radio data, MSX, and Spitzer images were used to determine some of the physical parameters of the region. We found 102 cluster member candidates in an area of about 3 × 3 square arcmin, the majority of them showing excess emission in the NIR. We found that IRAS 16571-4029 is formed by multiple infrared sources, all but one are associated with small groups of stars. This suggests that the fragmentation of massive molecular clouds generates the massive sub-clusters. We derived a mean visual extinction of A V = 12.8± 4.7 3.2. This result is independent of the assumed distance and agrees with the mean visual extinction A V = 14.4, as obtained by previous spectroscopic observations of two NIR sources in the direction of the IRAS 16571-4029 source. We also compare the results obtained in this study with those obtained in previous papers in this series finding a very good correlation between the number of cluster members N s and the cluster radius r c. The cluster radius varies from 0.2−0.3 pc (IRAS 15411-5352 and IRAS 16132-5039) until about 1 pc (IRAS 15408-5356). The youngest clusters are those associated with the RCW95 complex (IRAS 15408-5356 and IRAS 15411-5353) with ages in the range 1.5−2 × 10 6 years, while the sources associated with the RCW106 (IRAS 16132-5039, IRAS 16177-5018) and RCW116B (IRAS 16571-4029) complexes have ages in the range 2.5−3 × 10 6 years. The oldest of them is the cluster associated with the RCW121 region (IRAS 17149-4029), which has an estimated age of 4.2 × 10 6 years.
Monthly Notices of the Royal Astronomical Society, 2010
We report the results of visual spectroscopy, mid-infrared (MIR) mapping and photometry, and near infrared (NIR) photometry of two candidate symbiotic stars (IPHAS J193108.67+164950.5 and IPHAS J193709.65+202655.7) associated with extended MIR emission. Our analysis of the continua of these sources shows that they are likely to represent Class I-II young stellar objects (YSOs) in which most of the IR emission arises from circumstellar disks, and for which the physical characteristics (stellar temperatures, radii, masses and luminosities) are similar. The extended emission is characterised by a substantial increase in fluxes and dimensions to longer MIR wavelengths. This is likely to arise as a result of emission by polycyclic aromatic hydrocarbons (PAHs) within extended photodissociation regimes (PDRs), centred upon more compact ionized regions responsible for much of the shorter wave emission. Such dual emission structures are characteristic of those observed in many compact HII regions. Finally, we note that the clouds have asymmetrical structures and windswept morphologies, conceivably indicative of shock interaction with external winds. Where this is the case, then it is possible that the YSOs are located in regions of triggered star-formation.
IRAS 18317−0757: A Cluster of Embedded Massive Stars and Protostars
The Astrophysical Journal, 2004
We present high resolution, multiwavelength continuum and molecular line images of the massive star-forming region IRAS 18317−0757. The global infrared through millimeter spectral energy distribution can be approximated by a two temperature model (25K and 63K) with a total luminosity of approximately log(L/L ⊙ ) = 5.2. Previous submillimeter imaging resolved this region into a cluster of five dust cores, one of which is associated with the ultracompact H II region G23.955+0.150, and another with a water maser. In our new 2.7mm continuum image obtained with BIMA, only the UCH II region is detected, with total flux and morphology in good agreement with the free-free emission in the VLA centimeterwave maps. For the other four objects, the non-detections at 2.7mm and in the MSX mid-infrared bands are consistent with cool dust emission with a temperature of 13-40K and a luminosity of 1000-40000 L ⊙ . By combining single-dish and interferometric data, we have identified over two dozen virialized C 18 O cores in this region which contain ≈ 40% of the total molecular gas mass present. While the overall extent of the C 18 O and dust emission is similar, their emission peaks do not correlate well in detail. At least 11 of the 123 infrared stars identified by 2MASS in this region are likely to be associated with the star-forming cluster. Two of these objects (both associated with UCH II) were previously identified as O stars via infrared spectroscopy. Most of the rest of the reddened stars have no obvious correlation with the C 18 O cores or the dust continuum sources. In summary, our observations indicate that considerable fragmentation of the molecular cloud has taken place during the time required for the UCH II region to form and for the O stars to become detectable at infrared wavelengths. Additional star formation appears to be ongoing on the periphery of the central region where up to four B-type (proto)stars have formed amongst a substantial number of C 18 O cores.
The earliest stages of massive star formation: near and mid infrared observations
Astrophysics and Space Science, 2000
We present new near-IR and mid-IR images of relatively isolated massive star forming regions with a special emphasis on the candidate precursors to ultra-compact HII regions. These images reveal compact, almost circularly symmetric young stellar clusters, dominated by a single luminous massive member. The clusters indicate flattenned structures and dynamically unrelaxed states. In 4 of these young clusters we have discovered a nearly centrally located, prominent dark region visible at 2µm. 10µm images show examples where the dark region is associated with embedded luminous members of the cluster, as well as cases with no central 10µm source. The dark patches without embedded sources could be dense cores surviving inside the (proto?)clusters or left over wreckage from cluster formation. These images support current theoritical simulations of cluster formation.
An Infrared Survey of Isolated Nebular Structures at Galactic Latitudes 16.98° & 1.98° in ARAS map
Journal of Nepali Physical Society, 2019
Two isolated far infrared dust structures (∼2.61pc × 1.57pc and ∼82.99pc × 39.99pc) at galactic coordinates: (353.01˚, 16.98˚) and (18.42˚, 1.98˚), were selected. We adopted the distance of the first structure to be about 139 pc and that of the second structure to be 2.6 kpc. In this present work we have studied the flux density variation and calculated dust color temperature and mass profile of the dust and Jeans mass of the structures using the data reduction software ALADIN v9. Our aim was to test whether this region is star forming or not. We also calculated the size and inclination angle of our structures. The dust color temperature is found to lie in the range 20.75 K to 35.90 K for the first region and 22.52 K to 45.63 K for the second region. The total mass of gas for the first structure is found to be about 20.99 M ☉ and Jeans mass is found to be 180.9 M ☉ , which is significantly greater than the total mass of the structure, suggesting no possibility of star formation activity for the first region. For the second region, the total mass of gas and the Jeans mass are found to be 5621.61 M ☉ and 6005.04 M ☉ respectively. The mass of the region is still significantly lesser than the Jeans mass. Thus, we conclude that this region is also probably not a star forming region. Also the study of inclination angle suggests that the three-dimensional shape of structures is non uniform and regularly shaped.
The RMS survey: far-infrared photometry of young massive stars
Arxiv preprint arXiv: …, 2009
Context. The Red MSX Source (RMS) survey is a multi-wavelength campaign of follow-up observations of a colour-selected sample of candidate massive young stellar objects (MYSOs) in the galactic plane. This survey is returning the largest well-selected sample of MYSOs to date, while identifying other dust contaminant sources with similar mid-infrared colours including a large number of new ultra-compact (UC) H ii regions. Aims. To measure the far-infrared (IR) flux, which lies near the peak of the spectral energy distribution (SED) of MYSOs and UCH ii regions, so that, together with distance information, the luminosity of these sources can be obtained. Methods. Less than 50 % of RMS sources are associated with IRAS point sources with detections at 60 µm and 100 µm, though the vast majority are visible in Spitzer MIPSGAL or IRAS Galaxy Atlas (IGA) images. However, standard aperture photometry is not appropriate for these data due to crowding of sources and strong spatially variable far-IR background emission in the galactic plane. A new technique using a 2-dimensional fit to the background in an annulus around each source is therefore used to obtain far-IR photometry for young RMS sources. Results. Far-IR fluxes are obtained for a total of 1113 RMS candidates identified as young sources. Of these 734 have flux measurements using IGA 60 µm and 100 µm images and 724 using MIPSGAL 70 µm images, with 345 having measurements in both data sets.
Dust Characteristics of Massive Star‐forming Sites in the Mid‐Infrared
The Astrophysical Journal, 2001
Four massive star-forming regions were imaged in the mid-infrared with the MIRAC3 instrument : W51 IRS 2, Mon R2, DR 21, and S140. We obtained high spatial resolution (D1A) images at several wavelengths from 7.8 to 13.2 km with the circular variable Ðlter, as well as narrow-band continuum images at 12.5 and 20.6 km toward each region. In each massive star-forming region, one or more sources show deep silicate absorption. For at least two of the massive star-forming regions, W51 IRS 2 and Mon R2, the absorbing material is highly localized and may be circumstellar material in disks or shells. The silicate absorption occurs at least as often around massive young stars as around young stars of lower mass (which are more often observed). The estimated optical depths of the silicate features are consistent with those predicted by radiative transfer models toward ultracompact H II regions, but substantially higher than observed toward T Tauri stars and other low-mass young stellar objects. There is no consistent correspondence between silicate absorption and either the dust color temperature or the 12.5 km opacity. In W51 IRS 2, the two previously known mid-infrared sources have been resolved into at least six subsources. Infrared counterparts are newly reported for two radio-continuum sources in S140. Also, new mid-infrared sources have been detected in both W51 IRS 2 and S140. We suggest that the infrared source in the southwest of DR 21 may not be self-luminous, but may instead be heated by the three nearby radio continuum sources. The gas density in the ring at Mon R2 supports the blister scenario for the IRS 1 H II region.