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Post Info TOPIC: Proplyds
Blobrana


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Posts: 131433
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RE: Star Outer Disks
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Title: Formation and Evolution of Planetary Systems: Cold Outer Disks
Associated with Sun-like stars
Authors: Jinyoung Serena Kim, Dean C. Hines, Dana E. Backman, Lynne A.
Hillenbrand, Michael R. Meyer, Jens Rodmann, Amaya Moro-Martin, John M.
Carpenter, Murray D. Silverstone, Jeroen Bouwman, Eric E. Mamajek, Sebastian
Wolf, Renu Malhotra, Ilaria Pascucci, Joan Najita, Deborah L. Padgett, Thomas
Henning, Timothy Y. Brooke, Martin Cohen, Stephen E. Strom, Elizabeth B.
Stobie, Charles W. Engelbracht, Karl D. Gordon, Karl Misselt, Jane E.
Morrison, James Muzerolle, and Kate Y. L. Su

Researchers present the discovery of debris systems around three solar mass stars based upon observations performed with the Spitzer Space Telescope as part of a
Legacy Science Program, ''the Formation and Evolution of Planetary Systems''
(FEPS).
They also confirm the presence of debris around two other stars.
All the stars exhibit infrared emission in excess of the expected photospheres in the 70 micron band, but are consistent with photospheric emission at 33 micron.
This restricts the maximum temperature of debris in equilibrium with the stellar radiation to T not greater than 70 K.
They find that these sources are relatively old in the FEPS sample, in the age range 0.7 - 3 Gyr. Based on models of the spectral energy distributions, we suggest that these debris systems represent materials generated by collisions of planetesimal belts.
They speculate on the nature of these systems through comparisons to our own Kuiper Belt, and on the likely planet(s) responsible for stirring the system and ultimately releasing dust through collisions.
They further report observations of a nearby star HD 13974 (d =11 pc) that is indistinguishable from a bare photosphere at both 24 micron and 70 micron. The observations place strong upper limits on the presence of any cold dust in this nearby system (LIR/L* less than 10^ -5.2).

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-- Edited by Blobrana at 11:13, 2005-06-22

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Blobrana


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Posts: 131433
Date:
RE: Proplyds
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Using the Flamingos-I near-infrared imager at Gemini South, a UK/Japanese team of astronomers has imaged an outer region of the Trapezium Cluster near the centre of the Orion Nebula, and identified 396 sources.
Of these, 138 are brown dwarf candidates and 33 of those are candidate planetary mass objects. This could have an impact on our understanding of the initial mass function (IMF) for very low-mass bodies, especially in a hostile star forming environment.


Expand
Colour composite image from near-infrared J, H and K-band images including two of three fields observed in this Gemini South/Flamingos-I survey of the edge of the Trapezium Cluster at the core of the Orion Nebula.
This edge field was selected to avoid saturation of the core region due to the sensitivity/depth of these observations. Indicated on this image are the two bipolar nebulae (�blow-ups� right) discovered with this data. Also indicated (left of centre) is a grouping of six stars that is representative of a tendency for both stars and brown dwarfs to form in small groups of between four to eight sources.

The observations were made in J, H, and K bands during observing runs in 2001 and 2002. Three fields were imaged for one hour each in K and H bands and two hours in J. The depth of these data allowed the identification of a variety of new low-mass objects, and led to comparisons with other independent surveys of adjacent regions, resulting in statistically significant conclusions.
The survey`s results are expected to provide a wealth of targets for future research in this star-forming region due to its depth and resolution.
An ongoing study by the team is a spectroscopic follow-up with Gemini of the planetary mass objects (PMOs) of M less than 13 MJup.
Due to an increase in background contamination at this luminosity, the present study puts the upper limit of 3-13 MJup PMOs at 13% and likely at less than 10% of the cluster population (assuming an age of one million years for cluster members).

In addition to the identification of two new bipolar nebulae with bright central sources in the region, the study also found multiple trails and filaments that appear to be associated with low luminosity point sources. Others have no apparent point-source associations.
Another result of the survey analysis is that binary pairs of brown dwarfs and very low-mass stars (less than 0.1Msun) are less likely than more massive stars to have wide separations (greater than 150 AU) between them and any binary companions. When this is combined with an independent Subaru sample (of a different region in the Trapezium cluster), this relationship is confirmed to a 96% confidence level. Furthermore, a statistically very significant excess was found for both stars and brown dwarf pairs with small separations (6 arc seconds or 2,600 AU), which is consistent with the "ejected stellar embryo" hypothesis for brown dwarf formation.



A deep survey of brown dwarfs in Orion with Gemini
Authors: P.W.Lucas (1), P.F.Roche (2), M.Tamura (3) ((1) University of Hertfordshire, (2) University of Oxford, (3) NAOJ)

We report the results of a deep near infrared (JHK) survey of the outer parts of the Trapezium Cluster with Gemini South/Flamingos. 396 sources were detected in a 26 arcmin^2 area, including 138 brown dwarf candidates, defined as masses greater than 0.075 solar masses for an assumed age of 1 million years.
Only 33 of the brown dwarf candidates are planetary mass candidates (PMCs) with estimated masses in the range 0.003 and 0.012 solar masses. In an extinction limited sample (A(V) less than 5) complete to approximately 0.005 solar masses (5 Mjup) the mass function appears to drop by a factor of 2 at the deuterium burning threshold, i.e. at planetary masses.
After allowing for background contamination it is likely that planetary mass objects at 3-13 Jupiter masses number less than 10% of the cluster population, with an upper limit of 13%. Analysis of the spatial distribution of stars and brown dwarf candidates suggests that brown dwarfs and very low mass stars (less than 0.1 solar masses) are less likely than more massive stars to have wide (greater than150 AU) binary companions.
This result has modest statistical significance (96%) in our data but is supported at 93% confidence by analysis of a completely independent sample taken from the Subaru data of Kaifu et al.(2000).
There is a statistically very significant excess of both stars and brown dwarfs with small separations from each other (6 arcsec or 2600 AU). This appears to be due to the presence of small N subgroups, which are likely to be dynamically unstable in the long term. Hence these results are consistent with the 'ejected stellar embryo' hypothesis for brown dwarf formation.
We also report the discovery of two new bipolar nebulae, which are interpreted as Class I protostars.

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-- Edited by Blobrana at 01:02, 2005-06-21

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Posts: 131433
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Astronomers using the Submillimeter Array (SMA) on Mauna Kea, Hawaii, confirmed, for the first time, that many of the objects termed "
Proplyds" found in the Orion Nebula do have sufficient material to form new planetary systems like our own.



"The SMA is the only telescope that can measure the dust within the Orion proplyds, and thereby assess their true potential for forming planets. This is critical in our understanding of how solar systems form in hostile regions of space" - Jonathan Williams, University of Hawaii Institute for Astronomy, lead author on a paper submitted to The Astrophysical Journal.

Surviving in the chaotic regions within the Orion Nebula where stellar winds can reach a staggering two million miles per hour and temperatures exceed a searing 18,000 degrees Fahrenheit, the question remained - would enough material endure to form a new solar system or would it be eroded away into space like wind and sand eroding away desert cliffs?
It now appears that these protoplanetary disks are quite tenacious, bringing new grounds for optimism in the search for planetary systems.

Imaged by the Hubble Space Telescope back in the early 1990s as misshapen silhouettes against the nebular background, the most spectacular
proplyds appear bright. Their surrounding ionized cocoons glow due to their close proximity to a nearby hot star formation called the Trapezium.
The Trapezium is a star cluster consisting of more than 1,000 young, hot stars that are only 1 million years old. They condensed out of the original cold, dark cloud of gas that now glows from their ionizing light. They are crowded into a space about 4 light-years in diameter, the same as the distance between the Sun and Proxima Centauri, the next closest star in space.

Blasted by the solar winds of the Trapezium, the proplyds are the next generation of smaller stars to arise in Orion, this time with visible discs that may be forming planets. It has remained unclear, however, whether they contained enough material to form stable planetary systems.
Using the SMA, astronomers now have been able to probe deep inside these disks to measure their mass and to unravel the formation process presented by these potential infant solar systems.

"While the Hubble pictures were spectacular, they revealed only disk-like shapes that did not tell us the amount of material present" - David Wilner, Harvard-Smithsonian Centre for Astrophysics (CfA).
Since some of the discs appear to be comparable in size and mass to our own solar system, this strengthens the connection between the Orion proplyds and our origins.
Since most Sun-like stars in the Galaxy eventually form in environments like the Orion Nebula, the SMA results suggest that the formation of solar systems like our own is common and a continuing event in the Galaxy.

"The same cycle of birth, life and death we experience here on Earth is repeated in the stars overhead. Now, the SMA provides us with a front-row seat in unravelling the wonder of these cosmic events" - David Wilner.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Centre for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory.
CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

source


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