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Register a new userThe ISO-LWS map of the Serpens cloud core: I. The SEDs of the IR/SMM sources
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ISO-LWS mapping observations of the Serpens molecular cloud core are presented. The spectral range is 50 - 200 micron and the map size is 8 X 8. These observations suffer from severe source confusion at FIR wavelengths and we employ a Maximum Likelihood Method for the spectro-spatial deconvolution. The strong and fairly isolated source SMM1 FIRS1 presented a test case, whose modelled spectral energy distribution (SED), within observational errors, is identical to the observed one. The model results for the other infrared and submillimetre sources are therefore likely to represent their correct SEDs. Simulations demonstrating the reliability and potential of the developed method support this view. For the majority of sources the peak of the SEDs is found within the spectral range of the LWS and derived temperatures are generally higher (>30K) than have been found by earlier deconvolution attempts using IRAS data. SMM sizes are found to be only a few arcsec in diameter. In addition, the SMMs are generally optically thick even at LWS wavelengths. Self-consistent radiative transfer calculations indicates that the SMMs are optically thick out to even longer wavelengths. Models were calculated for five sources, for which sufficient data were available, viz. SMM 1, 2, 3, 4 and 9. These models are optically thick out to millimetre wavelengths (wavelength of unit optical depth 900 to 1400 micron). Envelope masses for these SMMs are in the range 2-6 Msun, which is of course considerably more massive than estimates based on the optically thin assumption. The luminosities are in the range 10-70 Lsun, suggesting the formation of low-mass to intermediate mass stars, so that the existence of such massive envelopes argues for extreme youth of the SMMs in the Serpens cloud core.
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We present spectrophotometric ISO imaging with the LWS and the CAM-CVF of the Serpens molecular cloud core. The LWS map is centred on the far infrared and submillimetre source SMM1 and its size is 8 x 8. The fine structure line emission in [OI] and [CII] is extended and can be successfully modelled to originate in a PDR with G_0 = 15 and n(H2) about 10^4 - 10^5 cm^-3. Extended emission is also observed in the rotational line emission of H2O and high-J CO. However, lack of sufficient angular resolution prevents us from excluding the possibility that the emssion regions of these lines are point like, which could be linked to the embedded objects SMM9 and SMM4. Toward the Class0 source SMM1, the LWS observations reveal, in addition to fine structure line emission, a rich spectrum of molecular lines. The sub-thermally excited and optically thick CO, H2O and OH lines are tracing an about 10^3 AU source with temperatures higher than 300 K and densities above 10^6 cm^-3. We show that geometry is of concern for the correct interpretation of the data and based on 2D-radiative transfer modelling of the disk/torus around SMM1, which successfully reproduces the entire observed SED and the observed line profiles of CO isotopomers, we can exclude the disk to be the source of the LWS-molecular line emission. The CAM-CVF permits us to see a region of rotational H2 emission. This H2 gas has a temperature of 10^3 K, which suggests that the heating of the gas is achieved through relatively slow shocks. Although we are not able to establish any firm conclusion regarding the detailed nature of the shock waves, our observations of the molecular line emission from SMM1 can be explainable in terms of an admixture of J-shocks and of C-shocks.
The Serpens cloud has received considerable attention in the last years, in particular the small region known as the Serpens cloud core where a plethora of star formation related phenomena are found. This review summarizes our current observational knowledge of the cloud, with emphasis on the core. Recent results are converging to a distance for the cloud of ~ 230 +- 20 pc, an issue which has been controversial over the years. We present the gas and dust properties of the cloud core and describe its structure and appearance at different wavelengths. The core contains a dense, very young, low mass stellar cluster with more than 300 objects in all evolutionary phases, from collapsing gaseous condensations to pre-main sequence stars. We describe the behaviour and spatial distribution of the different stellar populations (mm cores, Classes 0, I and II sources). The spatial concentration and the fraction number of Class 0/Class I/Class II sources is considerably larger in the Serpens core than in any other low mass star formation region, e.g. Taurus, Ophiuchus or Chamaeleon, as also stated in different works. Appropriate references for coordinates and fluxes of all Serpens objects are given. However, we provide for the first time a unified list of all near-IR sources which have up to now been identified as members of the Serpens core cluster; this list includes some members identified in this review. A cross-reference table of the near-IR objects with optical, mid-IR, submillimeter, radio continuum and X-ray surces is also provided. A simple analysis has allowed us to identify a sample of ~ 60 brown dwarf candidates among the 252 near-IR objects; some of them show near-IR excesses and, therefore, they constitute an attractive sample to study very young substellar objects. (abridged)
We present results from an ISOCAM survey in the two broad band filters LW2 (5-8.5 mu) and LW3 (12-18 mu) of a 0.13 square degree coverage of the Serpens Main Cloud Core. A total of 392 sources were detected in the 6.7 mu band and 139 in the 14.3 mu band to a limiting sensitivity of ~ 2 mJy. Only about 50% of the mid-IR excess sources show excesses in the near-IR J-H/H-K diagram. In the central Cloud Core the Class I/Class II number ratio is 19/18, i.e. about 10 times larger than in other young embedded clusters such as rho Ophiuchi or Chamaeleon. The mid-IR fluxes of the Class I and flat-spectrum sources are found to be on the average larger than those of Class II sources. Stellar luminosities are estimated for the Class II sample, and its luminosity function is compatible with a coeval population of about 2 Myr which follows a three segment power-law IMF. For this age about 20% of the Class IIs are found to be young brown dwarf candidates. The YSOs are in general strongly clustered, the Class I sources more than the Class II sources, and there is an indication of sub-clustering. The sub-clustering of the protostar candidates has a spatial scale of 0.12 pc. These sub-clusters are found along the NW-SE oriented ridge and in very good agreement with the location of dense cores traced by millimeter data. The smallest clustering scale for the Class II sources is about 0.25 pc, similar to what was found for rho Ophiuchi. Our data show evidence that star formation in Serpens has proceeded in several phases, and that a ``microburst of star formation has taken place very recently, probably within the last 10^5 yrs.
Context. Outflows provide indirect means to get an insight on diverse star formation associated phenomena. On scales of individual protostellar cores, outflows combined with intrinsic core properties can be used to study the mass accretion/ejection process of heavily embedded protostellar sources. Methods. An area comprising 460x230 of the Serpens cloud core has been mapped in 12 CO J = 3to 2 with the HARP-B heterodyne array at the James Clerk Maxwell Telescope; J = 3to 2 observations are more sensitive tracers of hot outflow gas than lower J CO transitions; combined with the high sensitivity of the HARP-B receptors outflows are sharply outlined, enabling their association with individual protostellar cores. Results. Most of ~20 observed outflows are found to be associated with known protostellar sources in bipolar or unipolar configurations. All but two outflow/core pairs in our sample tend to have a projected orientation spanning roughly NW-SE. The overall momentum driven by outflows in Serpens lies between 3.2 and 5.1 x 10^(-1) Modot km s^(-1), the kinetic energy from 4.3 to 6.7 x 10^(43) erg and momentum flux is between 2.8 and 4.4 x 10^(-4) Modot km s^(-1) yr^(-1). Bolometric luminosities of protostellar cores based on Spitzer photometry are found up to an order of magnitude lower than previous estimations derived with IRAS/ISO data. Conclusions. We confirm the validity of the existing correlations between the momentum flux and bolometric luminosity of Class I sources for the homogenous sample of Serpens, though we suggest that they should be revised by a shift to lower luminosities. All protostars classified as Class 0 sources stand well above the known Class I correlations, indicating a decline in momentum flux between the two classes.
(Abridged) The Long Wavelength Spectrometer (LWS) onboard the Infrared Space Observatory (ISO) observed the four large main-belt asteroids (1) Ceres, (2) Pallas, (4) Vesta, and (10) Hygiea multiple times. The photometric and spectroscopic data cover the wavelength range between 43 and 197 um, and are a unique dataset for future investigations and detailed characterisations of these bodies. The standard ISO archive products, produced through the last post-mission LWS pipeline, were still affected by instrument artefacts. Our goal was to provide the best possible data products to exploit the full scientific potential of these observations. We performed a refined reduction of all measurements, corrected for various instrumental effects, and re-calibrated the data. We outline the data reduction process and give an overview of the available data and the quality of the observations. We apply a thermophysical model to the flux measurements to derive far-IR based diameter and albedo values of the asteroids. The measured thermal rotational lightcurve of (4) Vesta is compared to model predictions. The absolute photometric accuracy of the data products was foubd to be better than 10%. The calibrated spectra will serve as source for future mineralogical studies of dwarf planets and dwarf planet candidates.
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