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Stellar Sparklers That Last

While fireworks only last a short time here on Earth, a bundle of cosmic sparklers in a nearby cluster of stars will be going off for a very long time. NGC 1333 is a star cluster populated with many young stars that are less than 2 million years old -- a blink of an eye in astronomical terms for stars like these expected to burn for billions of years.
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Title: The JCMT Gould Belt Survey: SCUBA-2 observations of radiative feedback in NGC1333
Authors: J. Hatchell, T. Wilson, E. Drabek, E. Curtis, J. Richer, D. Nutter, J. Di Francesco, D. Ward-Thompson on behalf of the JCMT GBS consortium

We present observations of NGC1333 from SCUBA-2 on JCMT, observed as a JCMT Gould Belt Survey pilot project during the shared risk campaign when the first of four arrays was installed at each of 450 and 850 microns. Temperature maps are derived from 450 micron and 850 micron ratios under the assumption of constant dust opacity spectral index beta=1.8. Temperatures indicate that the dust in the northern (IRAS 6/8) region of NGC1333 is hot, 20-40 K, due to heating by the B star SVS3, other young stars in the IR/optically visible cluster, and embedded protostars. Other luminous protostars are also identified by temperature rises at the 17" resolution of the ratio maps (0.02 pc assuming a distance of 250 pc for Perseus). The extensive heating raises the possibility that the radiative feedback may lead to increased masses for the next generation of stars.

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"Failed Stars" Galore with One Youngster Only Six Times Heftier than Jupiter

An international team of astronomers has discovered over two-dozen new free-floating brown dwarfs that reside in two young star clusters. One brown dwarf is a lightweight youngster only about six times heftier than Jupiter. What's more, one cluster contains a surprising surplus of brown dwarfs; it harbours half as many of these astronomical oddballs as normal stars. These findings come from deep surveys and extensive follow-up observations using the Subaru Telescope in Hawaii and the Very Large Telescope (VLT) in Chile, two of the world's largest optical-infrared telescopes.
Sometimes described as failed stars, brown dwarfs are unusual celestial objects that straddle the boundary between stars and planets. When young, they glow brightly from the heat of formation, but they eventually cool down and end up with atmospheres that exhibit planet-like characteristics.

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Title: Substellar Objects in Nearby Young Clusters (SONYC) IV: A census of very low mass objects in NGC1333
Authors: Aleks Scholz (DIAS), Koraljka Muzic (Toronto), Vincent Geers (Zurich), Mariangela Bonavita (Toronto), Ray Jayawardhana (Toronto), Motohide Tamura (NAOJ)

SONYC -- Substellar Objects in Nearby Young Clusters -- is a program to investigate the frequency and properties of young substellar objects with masses down to a few times that of Jupiter. Here we present a census of very low mass objects in the ~1 Myr old cluster NGC1333. We analyse near-infrared spectra taken with FMOS/Subaru for 100 candidates from our deep, wide-field survey and find 10 new likely brown dwarfs with spectral types of M6 or later. Among them, there are three with >~M9 and one with early L spectral type, corresponding to masses of 0.006 to <~0.02 Msol, so far the lowest mass objects identified in this cluster. The combination of survey depth, spatial coverage, and extensive spectroscopic follow-up makes NGC1333 one of the most comprehensively surveyed clusters for substellar objects. In total, there are now 51 objects with spectral type M5 or later and/or effective temperature of 3200 K or cooler identified in NGC1333; 30-40 of them are likely to be substellar. NGC1333 harbours about half as many brown dwarfs as stars, which is significantly more than in other well-studied star forming regions, thus raising the possibility of environmental differences in the formation of substellar objects. The brown dwarfs in NGC1333 are spatially strongly clustered within a radius of ~1 pc, mirroring the distribution of the stars. The disk fraction in the substellar regime is <66%, lower than for the total population (83%) but comparable to the brown dwarf disk fraction in other 2-3 Myr old regions.

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NGC 1333
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Title: Spitzer Observations of NGC 1333: A Study of Structure and Evolution in a Nearby Embedded Cluster
Authors: R. A. Gutermuth, P. C. Myers, S. T. Megeath, L. E. Allen, J. L. Pipher, J. Muzerolle, A. Porras, E. Winston, G. Fazio
(Version v2)

We present a comprehensive analysis of structure in the young, embedded cluster, NGC 1333 using members identified with Spitzer and 2MASS photometry based on their IR-excess emission. In total, 137 members are identified in this way, composed of 39 protostars and 98 more evolved pre-main sequence stars with disks. Of the latter class, four are transition/debris disk candidates. The fraction of exposed pre-main sequence stars with disks is 83% 11%, showing that there is a measurable diskless pre-main sequence population. The sources in each of the Class I and Class II evolutionary states are shown to have very different spatial distributions relative to the distribution of the dense gas in their natal cloud. However, the distribution of nearest neighbour spacings among these two groups of sources are found to be quite similar, with a strong peak at spacings of 0.045 pc. Radial and azimuthal density profiles and surface density maps computed from the identified YSOs show that NGC 1333 is elongated and not strongly centrally concentrated, confirming previous claims in the literature. We interpret these new results as signs of a low velocity dispersion, extremely young cluster that is not in virial equilibrium.

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Title: A Spectroscopic Study of Young Stellar Objects in the Serpens Cloud Core and NGC 1333
Authors: E. Winston, S.T. Megeath, S.J. Wolk, J. Hernandez, R. Gutermuth, J. Muzerolle, J.L. Hora, K. Covey, L.E. Allen, B. Spitzbart, D. Peterson, P. Myers, G.G. Fazio

We present spectral observations of 130 young stellar objects (YSOs) in the Serpens Cloud Core and NGC 1333 embedded clusters. The observations consist of near-IR spectra in the H and K-bands, from SpeX on the IRTF and far-red spectra (6000 - 9000 A) from Hectospec on the MMT. These YSOs were identified in previous Spitzer and Chandra observations, and the evolutionary classes of the YSOs were determined from the Spitzer mid-IR photometry. With these spectra, we search for corroborating evidence for the pre-main sequence nature of the objects, study the properties of the detected emission lines as a function of evolutionary class, and obtain spectral types for the observed YSOs. By comparing the positions of the YSOs in the HR diagrams with the pre-main sequence tracks of Baraffe (1998), we determine ages of the embedded sources and study the relative ages of the YSOs with and without optically thick circumstellar disks. The apparent isochronal ages of the YSOs in both clusters range from less than 1 Myr to 10 Myr, with most objects below 3 Myr. The observed distribution of ages for the Class II and Class III objects are statistically indistinguishable. We examine the spatial distribution and extinction of the YSOs as a function of their isochronal ages. We find the sources < 3 Myr to be concentrated in the molecular cloud gas while the older sources are spatially dispersed and are not deeply embedded. Nonetheless, the sources with isochronal ages > 3 Myr show all the characteristics of young stellar objects in their spectra, their IR spectral energy distributions, and their X-ray emission.

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Title: Spitzer Observations of NGC 1333: A Study of Structure and Evolution in a Nearby Embedded Cluster
Authors: R. A. Gutermuth, P. C. Myers, S. T. Megeath, L. E. Allen, J. L. Pipher, J. Muzerolle, A. Porras, E. Winston, G. Fazio

We present a comprehensive analysis of structure in the young, embedded cluster, NGC 1333 using members identified with Spitzer and 2MASS photometry based on their IR-excess emission. In total, 137 members are identified in this way, composed of 39 protostars and 98 more evolved pre-main sequence stars with disks. Of the latter class, four are transition/debris disk candidates. The fraction of exposed pre-main sequence stars with disks is 83% 11%, showing that there is a measurable diskless pre-main sequence population. The sources in each of the Class I and Class II evolutionary states are shown to have very different spatial distributions relative to the distribution of the dense gas in their natal cloud. However, the distribution of nearest neighbour spacings among these two groups of sources are found to be quite similar, with a strong peak at spacings of 0.045 pc. Radial and azimuthal density profiles and surface density maps computed from the identified YSOs show that NGC 1333 is elongated and not strongly centrally concentrated, confirming previous claims in the literature. We interpret these new results as signs of a low velocity dispersion, extremely young cluster that is not in virial equilibrium.

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Title: HST/NICMOS Observations of NGC 1333: The Ratio of Stars to Sub-Stellar Objects
Authors: Julia Greissl, Michael R. Meyer, Bruce A. Wilking, Tina Fanetti, Glenn Schneider, Thomas P. Greene, Erick Young

We present an analysis of NICMOS photometry and low-resolution grism spectroscopy of low-mass stars and sub-stellar objects in the young star-forming region NGC 1333. Our goal is to constrain the ratio of low-mass stars to sub- stellar objects down to 20 Mjup in the cluster as well as constrain the cluster IMF down to 30 Mjup in combination with a previous survey of NGC 1333 by Wilking et al. Our survey covers 4 fields of 51.2" x 51.2", centred on brown dwarf candidates previously identified in Wilking et al. We extend previous work based on the use of a water vapour index for spectral typing to wavelengths accessible with NICMOS on the HST. Spectral types were derived for the 14 brightest objects in our fields, ranging from < M0 - M8, which at the age of the cluster (0.3 Myr) corresponds to a range in mass of > 0.25 - 0.02 Msun. In addition to the spectra, we present an analysis of the colour-magnitude diagram using pre-main sequence evolutionary models of D'Antona & Mazzitelli. Using an extinction-limited sample, we derive the ratio of low-mass stars to brown dwarfs. Comparisons of the observed ratio to that expected from the field IMF of Chabrier indicate that the two results are consistent. We combine our data with that of Wilking et al. to compute the ratio of intermediate-mass stars (0.1 - 1.0 Msun) to low-mass objects (0.03 - 0.1 Msun) in the cluster. We also report the discovery of a faint companion to the previously confirmed brown dwarf ASR 28, as well as a possible outflow surrounding ASR 16. If the faint companion is confirmed as a cluster member, it would have a mass of ~ 5 Mjup (mass ratio 0.15) at a projected distance of 350 AU, similar to 2MASS 1207-3923 B.

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-- Edited by Blobrana at 12:38, 2006-11-17

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A Large Scale Survey of NGC1333
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Title: A Large Scale Survey of NGC1333
Authors: Andrew J. Walsh, Philip C. Myers, James Di Francesco, Subhanjoy Mohanty, Tyler L. Bourke, Robert Gutermuth, David Wilner

We observed the clustered star forming complex NGC1333 with the BIMA and FCRAO telescopes in the transitions HCO+(1-0) and N2H+(1-0) over an 11'x11' area with resolution ~10" (0.015pc). The N2H+ emission follows very closely the submillimeter dust continuum emission, while HCO+ emission appears more spatially extended and also traces outflows. We have identified 93 N2H+ cores using the CLUMPFIND algorithm, and we derive N2H+ core masses between 0.05 and 2.5M_sun, with uncertainties of a factor of a few, dominated by the adopted N2H+ abundance. From a comparison with virial masses, we argue that most of these N2H+ cores are likely to be bound, even at the lowest masses, suggesting that the cores do not trace transient structures, and implies the entire mass distribution consists of objects that can potentially form stars. We find that the mass distribution of N2H+ cores resembles the field star IMF, which suggests that the IMF is locked in at the pre-stellar stage of evolution. We find that the N2H+ cores associated with stars identified from Spitzer infrared images have a flat mass distribution. This might be because lower mass cores lose a larger fraction of their mass when forming a star. Even in this clustered environment, we find no evidence for ballistic motions of the cores relative to their lower density surroundings traced by isotopic CO emission, though this conclusion must remain tentative until the surroundings are observed at the same high resolution as the N2H+.

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NGC1333
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Credit NASA

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