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تسجيل مستخدم جديدSurface density of the young cluster IC 348 in the Perseus molecular cloud
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The IC 348 young star cluster contains more than 300 confirmed members. It is embedded in the Perseus molecular cloud, making any clustering analysis subject to an extinction bias. In this work, we derive the extinction map of the cloud and revisit the content of IC 348 through a statistical approach that uses the 2MASS data. Our goal was to address the question of the completeness of IC 348 and of young clusters in general. We performed a combined analysis of the star color and density in this region, in order to establish the surface density map of the cluster. We reached the conclusion that IC 348 has structures up to 25 from the cluster center, and we estimate that about 40 members brighter than Ks=13 mag are still unidentified. Although we cannot use our statistical method to identify these new members individually, the surface density map gives a strong indication of their actual location. They are distributed in the outer regions of the cluster, where very few dedicated observations have been made so far, which is probably why they escaped previous identification. In addition, we propose the existence of a new embedded cluster associated to the infrared source MSX6C G160.2784-18.4216, about 38 south of IC 348.
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In this paper we discuss the physical conditions of clumpy nature in the IC 348 molecular cloud. We combine new observations of fully sampled maps in [C I] at 492 GHz and 12CO 4--3, taken with the KOSMA 3 m telescope at about 1 resolution, with FCR
AO data of 12CO 1--0, 13CO 1--0 and far-infrared continuum data observed by HIRES/IRAS. To derive the physical parameters of the region we analyze the three different line ratios. A first rough estimate of abundance is obtained from an LTE analysis. To understand the [C I] and CO emission from the PDRs in IC 348, we use a clumpy PDR model. With an ensemble of identical clumps, we constrain the total mass from the observed absolute intensities. Then we apply a more realistic clump distribution model with a power law index of 1.8 for clump-mass spectrum and a power law index of 2.3 for mass-size relation. We provide detailed fits to observations at seven representative positions in the cloud, revealing clump densities between 4 10$^{4}$ cm$^{-3}$ and 4 10$^{5}$ cm$^{-3}$ and C/CO column density ratios between 0.02 and 0.26. The derived FUV flux from the model fit is consistent with the field calculated from FIR continuum data, varying between 2 and 100 Draine units across the cloud. We find that both an ensemble of identical clumps and an ensemble with a power law clump mass distribution produce line intensities which are in good agreement (within a factor ~ 2) with the observed intensities. The models confirm the anti-correlation between the C/CO abundance ratio and the hydrogen column density found in many regions.
We report on a near-infrared adaptive optics survey of a sample of 66 low-mass members of the pre-main sequence stellar cluster IC 348. We find 12 binary systems in the separation range 0.1-8.0 arcsec. An estimate of the number of faint undetected co
mpanions is derived, before we evaluate the binary frequency in this cluster. In the orbital period range log P=5.0-7.9 days, the binary fraction in IC 348 is 19+/-5 %.This is similar to the values correspondings to G- and M-dwarfs populations in the solar neigbourhood. Substellar companions are found to be rare, or even missing, as companions of low-mass stars in the separation range we surveyed. Also, the mass ratio distribution is not peaked at q=1. We do not find any evidence for an evolution of the binary frequency with age within the age spread of the cluster of about 10 Myr. We conclude that there is no temporal evolution of the binary fraction between a few Myrs after the formation process, the zero-age main sequence and the field population. We find instead a trend for the binary fraction to be inversely correlated with stellar density, with only loose associations exhibiting an excess of binaries. Either all star-forming regions initially host a large number of binaries, which is subsequently reduced only in dense clusters on a timescale of less than 1 Myr due to numerous gravitational encounters, or specific initial conditions in the parental molecular clouds impact on the fragmentation process leading to intrinsically different binary fractions.
In this paper, we address two issues related to primordial disk evolution in three clusters (NGC 1333, IC 348, and Orion A) observed by the INfrared Spectra of Young Nebulous Clusters (IN-SYNC) project. First, in each cluster, averaged over the sprea
d of age, we investigate how disk lifetime is dependent on stellar mass. The general relation in IC 348 and Orion A is that primordial disks around intermediate mass stars (2--5$M_{odot}$) evolve faster than those around loss mass stars (0.1--1$M_{odot}$), which is consistent with previous results. However, considering only low mass stars, we do not find a significant dependence of disk frequency on stellar mass. These results can help to better constrain theories on gas giant planet formation timescales. Secondly, in the Orion A molecular cloud, in the mass range of 0.35--0.7$M_{odot}$, we provide the most robust evidence to date for disk evolution within a single cluster exhibiting modest age spread. By using surface gravity as an age indicator and employing 4.5 $mu m$ excess as a primordial disk diagnostic, we observe a trend of decreasing disk frequency for older stars. The detection of intra-cluster disk evolution in NGC 1333 and IC 348 is tentative, since the slight decrease of disk frequency for older stars is a less than 1-$sigma$ effect.
IC 1274 is a faintly luminous nebula lying on the near surface of the Lynds 227 (L227) molecular cloud. Four luminous, early-type (B0-B5) stars are located within a spherical volume ~5 in diameter that appears to be clear of heavy obscuration. Approx
imately centered in the cleared region is the B0 V star HD 166033, which is thought to be largely responsible for the cavitys excavation. Over 80 H-alpha emission sources brighter than V~21 have been identified in the region. More than half of these are concentrated in IC 1274 and are presumably members of a faint T Tauri star population. Chandra Advanced CCD Imaging Spectrometer (ACIS) imaging of a nearby suspected pulsar and time-variable gamma-ray source (GeV J1809-2327) detected 21 X-ray sources in the cluster vicinity, some of which are coincident with the early-type stars and H-alpha emitters in IC 1274. Deep (V~22) optical BVRI photometry has been obtained for the cluster region. A distance of 1.82 +/- 0.3 kpc and a mean extinction of Av ~1.21 +/- 0.2 mag follow from photometry of the early-type stars. Using pre-main-sequence evolutionary models, we derive a median age for the H-alpha emitters and X-ray sources of ~1 Myr; however, a significant dispersion is present. Our interpretation of the structure of IC 1274 is that the early-type stars formed recently and are in the process of dispersing the molecular gas on the near surface of L227. The displaced material was driven against what remains of the molecular cloud to the east, enabling the formation of the substantial number of T Tauri stars found there. We identify a V~21.5 star very near the position of X-ray source 5, the assumed gamma-ray source and young pulsar candidate. The lack of distinctive characteristics for this source, however, coupled with the density of faint stars in this region suggest that this may be a random superposition.
We compare the statistical properties of J=1-0 13CO spectra observed in the Perseus Molecular Cloud with synthetic J=1-0 13CO spectra, computed solving the non-LTE radiative transfer problem for a model cloud obtained as solutions of the three dimens
ional magneto-hydrodynamic (MHD) equations. The model cloud is a randomly forced super-Alfvenic and highly super-sonic turbulent isothermal flow. The purpose of the present work is to test if idealized turbulent flows, without self-gravity, stellar radiation, stellar outflows, or any other effect of star formation, are inconsistent or not with statistical properties of star forming molecular clouds. We present several statistical results that demonstrate remarkable similarity between real data and the synthetic cloud. Statistical properties of molecular clouds like Perseus are appropriately described by random super-sonic and super-Alfvenic MHD flows. Although the description of gravity and stellar radiation are essential to understand the formation of single protostars and the effects of star formation in the cloud dynamics, the overall description of the cloud and of the initial conditions for star formation can apparently be provided on intermediate scales without accounting for gravity, stellar radiation, and a detailed modeling of stellar outflows. We also show that the relation between equivalent line width and integrated antenna temperature indicates the presence of a relatively strong magnetic field in the core B1, in agreement with Zeeman splitting measurements.
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