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NGC 2264
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Title: The Distance to NGC 2264
Authors: Eric J. Baxter, Kevin R. Covey, August A. Muench, Gabor Furesz, Luisa Rebull, Andrew H. Szentgyorgyi

We determine the distance to the open cluster NGC 2264 using a statistical analysis of cluster member inclinations. We derive distance-dependent values of sin i (where i is the inclination angle) for 97 stars in NGC 2264 from the rotation periods, luminosities, effective temperatures, and projected equatorial rotation velocities, v sin i, measured for these stars. We have measured 96 of the v sin i values in our sample by analysing high-resolution spectra with a cross-correlation technique. We model the observed distribution of sin i for the cluster by assuming that member stars have random axial orientations and by adopting prescriptions for the measurement errors in our sample. By adjusting the distance assumed in the observed sin i distribution until it matches the modelled distribution, we obtain a best-fit distance for the cluster. We find the data to be consistent with a distance to NGC 2264 of 913 pc. Quantitative tests of our analysis reveals uncertainties of 40 and 110 pc due to sampling and systematic effects, respectively. This distance estimate suggests a revised age for the cluster of 1.5 Myrs, although more detailed investigations of the full cluster membership are required to draw strong conclusions.

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Title: A Spitzer View of the Young Open Cluster NGC 2264
Authors: Hwankyung Sung (Sejong Univ., Korea) John R. Stauffer (SSC, Caltech, USA) Mike S. Bessell (MSSSO, ANU, Australia)

We have performed mid-IR photometry of the young open cluster NGC 2264 using the images obtained with the Spitzer Space Telescope IRAC and MIPS instruments and present a normalised classification scheme of young stellar objects in various colour-colour diagrams to make full use of the information from multicolour photometry. These results are compared with the classification scheme based on the slope of the spectral energy distribution (SED).
From the spatial distributions of Class I and II stars, we have identified two subclusterings of Class I objects in the CONE region of Sung et al. The disked stars in the other star forming region S MON are mostly Class II objects. These three regions show a distinct difference in the fractional distribution of SED slopes as well as the mean value of SED slopes. The fraction of stars with primordial disks is nearly flat between log m = 0.2 -- -0.5, and that of transition disks is very high for solar mass stars. In addition, we have derived a somewhat higher value of the primordial disk fraction for NGC 2264 members located below the main pre-main sequence locus (so-called BMS stars). This result supports the idea that BMS stars are young stars with nearly edge-on disks. We have also found that the fraction of primordial disks is very low near the most massive star S Mon and increases with distance from S Mon.

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Christmas Tree cluster
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Known as the Christmas Tree cluster, this colourful collection of stars lies 2,600 light-years from Earth in the constellation of Monoceros, the unicorn.

NGC2264b.jpg
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Credit Max Planck Society/ESO

The cluster was first discovered in the 18th century but was captured anew in this stunning image by by the 2.2-meter Max Planck Society/ESO telescope at La Silla observatory in the Atacama Desert.

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Posts: 129106
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NGC 2264
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The festive season has arrived for astronomers at the European Southern Observatory (ESO) in the form of this dramatic new image. It shows the swirling gas around the region known as NGC 2264 - an area of sky that includes the sparkling blue baubles of the Christmas Tree star cluster.
NGC 2264 lies about 2600 light-years from Earth in the obscure constellation of Monoceros, the Unicorn, not far from the more familiar figure of Orion, the Hunter. The image shows a region of space about 30 light-years across.
William Herschel discovered this fascinating object during his great sky surveys in the late 18th century. He first noticed the bright cluster in January 1784 and the brightest part of the visually more elusive smudge of the glowing gas clouds at Christmas nearly two years later. The cluster is very bright and can easily be seen with binoculars. With a small telescope (whose lenses will turn the view upside down) the stars resemble the glittering lights on a Christmas tree. The dazzling star at the top is even bright enough to be seen with the unaided eye. It is a massive multiple star system that only emerged from the dust and gas a few million years ago.

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RE: NGC2264
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Title: Spitzer imaging of the jet driving the NGC 2264 G outflow
Authors: Paula S. Teixeira (1,2,3), Carolyn McCoey (4), Michael Fich (4), Charles J. Lada (1), ((1) Harvard-Smithsonian Center for Astrophysics, (2) Departamento de Fisica da Faculdade de Ciencias da Universidade de Lisboa, Portugal, (3) Laboratorio Associado Instituto D. Luiz - SIM, Universidade de Lisboa, Portugal, (4) Department of Physics & Astronomy, University of Waterloo, Waterloo, Canada)

We present new infrared imaging of the NGC 2264 G protostellar outflow region, obtained with the InfraRed Array Camera (IRAC) on-board the Spitzer Space Telescope. A jet in the red outflow lobe (eastern lobe) is clearly detected in all four IRAC bands and, for the first time, is shown to continuously extend over the entire length of the red outflow lobe traced by CO observations. The redshifted jet also extends to a deeply embedded Class 0 source, VLA 2, confirming previous suggestions that it is the driving source of the outflow (Gomez et al. 1994). The images show that the easternmost part of the redshifted jet exhibits what appear to be multiple changes of direction. To understand the redshifted jet morphology we explore several mechanisms that could generate such apparent changes of direction. From this analysis, we conclude that the redshifted jet structure and morphology visible in the IRAC images can be largely, although not entirely, explained by a slowly precessing jet (period ~8000 yr) that lies mostly on the plane of the sky. It appears that the observed changes in the redshifted jet direction may be sufficient to account for a significant fraction of the broadening of the outflow lobe observed in the CO emission.

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Astronomers using the Spitzer Space Telescope have captured a spectacular new picture of a star-forming region called the "Christmas Tree Cluster," complete with first-ever views of a group of newborn stars still linked to their siblings.

Spitzer's cameras are very sensitive to the infrared (heat), allowing astronomers to see through the obscuring gas and dust of the star-forming cloud that surrounds infant stars.
The Christmas Tree Cluster, also known as NGC 2264, is a well-studied region in the Monoceros (the Unicorn) constellation. The Christmas Tree Cluster was so named because it looks like a pinetree in visible light. The nebula is roughly 2,500 light-years away.


Position(2000): RA = 06 : 41.1 Dec = +09 : 53

"This region has it all. We see the dramatic-looking emission of cold gas -- clouds that look like thunderheads. We see when the massive molecular cloud breaks up and begins to condense into clumps of stars. And, for the first time, because of Spitzer's sensitivity, we can see individual stars roughly the size of our sun tightly packed within those clumps" - Erick T. Young, University of Arizona.

The cluster of stars is so tightly packed that they must be less than 100,000 years old.
Astronomers are calling this compact collection of bright protostars within the Christmas Tree Cluster the "Snowflake Cluster" because of how they are spaced. The newborn stars are patterned like a single feathery crystal of snow, or geometrically spaced like spokes in a wheel.
The Spitzer observations show that just as theory predicts, the density and temperature of the initial star-forming cloud dictates the spacing between the protostars.

Young is deputy principal investigator for Spitzer's Multiband Imaging Photometer (MIPS), a UA-built camera that took the longest wavelengths of infrared light used in Christmas Tree Cluster mosaic. Astronomers combined light from MIPS and Spitzer's Infrared Array Camera (IRAC), developed by the Smithsonian Astrophysical Observatory, in constructing in the picture.

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