The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
S T Megeath - One of the best experts on this subject based on the ideXlab platform.
-
the spitzer space telescope survey of the orion a and b molecular clouds ii the spatial distribution and demographics of dusty young stellar objects
The Astronomical Journal, 2015Co-Authors: S T Megeath, R A Gutermuth, J Muzerolle, E Kryukova, J L Hora, L E Allen, K M Flaherty, Lee Hartmann, Philip C MyersAbstract:We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc^(−2) to over 10,000 pc^(−2), with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities ≥10 pc^(−2), we find that 59% of the YSOs are in the largest cluster, the Orion Nebula Cluster (ONC), while 13% of the YSOs are found in a Distributed Population. A lower fraction of protostars in the Distributed Population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups shows that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only ~2 Myr in age. We find that the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or dynamical interactions in dense, clustered regions.
-
the spitzer space telescope survey of the orion a and b molecular clouds ii the spatial distribution and demographics of dusty young stellar objects
arXiv: Astrophysics of Galaxies, 2015Co-Authors: S T Megeath, R A Gutermuth, J Muzerolle, E Kryukova, J L Hora, L E Allen, K M Flaherty, Lee Hartmann, Philip C MyersAbstract:We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc$^{-2}$ to over 10,000 pc$^{-2}$, with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities $\ge10$ pc$^{-2}$, we find that 59% of the YSOs are in the largest cluster, the Orion Nebular Cluster (ONC), while 13% of the YSOs are found in a Distributed Population. A lower fraction of protostars in the Distributed Population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups show that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only $\sim 2$ Myr in age. We find the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or by dynamical interactions in dense, clustered regions.
John M. Carpenter - One of the best experts on this subject based on the ideXlab platform.
-
a Distributed Population of low mass pre main sequence stars near the taurus molecular clouds
arXiv: Astrophysics, 2006Co-Authors: Catherine L. Slesnick, John M. Carpenter, Lynne A. Hillenbrand, Eric E. MamajekAbstract:We present a drift scan survey covering a ~5 deg by 50 deg region toward the southern portion of the Taurus-Auriga molecular cloud. Data taken in the B,R,I filters with the Quest-2 camera on the Palomar 48-inch telescope were combined with 2MASS near-infrared photometry to select candidate young stars. Follow-up optical spectroscopy of 190 candidates led to identification of 42 new low mass pre-main sequence stars with spectral types M4-M8, of which approximately half exhibit surface gravity signatures similar to known Taurus stars while the other half exhibit surface gravity signatures similar to members of the somewhat older Upper Sco, TW Hya and Beta Pic associations. The pre-main sequence stars are spread over ~35 deg, and many are located well outside of previously explored regions. From assessment of the spatial and proper motion distributions, we argue that the new pre-main sequence stars identified far from the clouds cannot have originated from the vicinity of the 1-2 Myr-old subclusters which contain the bulk of the identified Taurus members, but instead represent a newly-identified area of recent star-formation near the clouds.
-
A Distributed Population OF LOW-MASS PRE-MAIN-SEQUENCE STARS NEAR THE TAURUS MOLECULAR CLOUDS
The Astronomical Journal, 2006Co-Authors: Catherine L. Slesnick, John M. Carpenter, Lynne A. Hillenbrand, Eric E. MamajekAbstract:We present a drift-scan survey covering a ~5° × 50° region toward the southern portion of the Taurus-Auriga molecular cloud. Data taken in the B,R,I filters with the Quest-2 camera on the Palomar 48 inch (1.2 m) Samuel Oschin Telescope were combined with Two Micron All Sky Survey near-infrared photometry to select candidate young stars. Follow-up optical spectroscopy of 190 candidates led to the identification of 42 new low-mass pre-main-sequence stars with spectral types M4-M8, of which approximately half exhibit surface gravity signatures similar to known Taurus stars, while the other half exhibit surface gravity signatures similar to members of the somewhat older Upper Scorpius, TW Hya, and β Pic associations. The pre-main-sequence stars are spread over ~35°, and many are located well outside of previously explored regions. From assessment of the spatial and proper-motion distributions, we argue that the new pre-main-sequence stars identified far from the clouds cannot have originated from the vicinity of the 1-2 Myr old subclusters that contain the bulk of the identified Taurus members but instead represent a newly identified area of recent star formation near the clouds.
-
2MASS Observations of the Perseus, Orion A, Orion B, and Monoceros R2 Molecular Clouds
The Astronomical Journal, 2000Co-Authors: John M. CarpenterAbstract:We use the 2MASS Second Incremental Release Point Source Catalog to investigate the spatial distribution of young stars in the Perseus, Orion A, Orion B, and MonR2 molecular clouds. After subtracting a semiempirical model of the field star contamination from the observed star counts, stellar surface density maps are used to identify compact clusters and any stellar Population found more uniformly Distributed over the molecular cloud. Each cloud contains between two and seven clusters, with at least half of the cluster Population found in a single, rich cluster. In addition, a Distributed stellar Population is inferred in the Orion A and MonR2 molecular clouds within the uncertainties of the field star subtraction with a surface density between 0.013 and 0.083 arcmin-2. Sensitivity calculations suggest, however, that the number of stars in the Distributed Population may be underestimated by a factor of 2 or more if stars have been forming with a Miller-Scalo IMF at a constant star formation rate for longer than 10 Myr. After considering the possible evolutionary status of the Distributed Population, the global star formation efficiency implied by the sum of the Distributed and cluster Populations ranges between 1% and 9% among the four clouds. The fraction of the total stellar Population contained in clusters for the nominal extinction model ranges from ≈50% to 100% if the Distributed Population is relatively young (
Philip C Myers - One of the best experts on this subject based on the ideXlab platform.
-
the spitzer space telescope survey of the orion a and b molecular clouds ii the spatial distribution and demographics of dusty young stellar objects
The Astronomical Journal, 2015Co-Authors: S T Megeath, R A Gutermuth, J Muzerolle, E Kryukova, J L Hora, L E Allen, K M Flaherty, Lee Hartmann, Philip C MyersAbstract:We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc^(−2) to over 10,000 pc^(−2), with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities ≥10 pc^(−2), we find that 59% of the YSOs are in the largest cluster, the Orion Nebula Cluster (ONC), while 13% of the YSOs are found in a Distributed Population. A lower fraction of protostars in the Distributed Population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups shows that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only ~2 Myr in age. We find that the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or dynamical interactions in dense, clustered regions.
-
the spitzer space telescope survey of the orion a and b molecular clouds ii the spatial distribution and demographics of dusty young stellar objects
arXiv: Astrophysics of Galaxies, 2015Co-Authors: S T Megeath, R A Gutermuth, J Muzerolle, E Kryukova, J L Hora, L E Allen, K M Flaherty, Lee Hartmann, Philip C MyersAbstract:We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc$^{-2}$ to over 10,000 pc$^{-2}$, with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities $\ge10$ pc$^{-2}$, we find that 59% of the YSOs are in the largest cluster, the Orion Nebular Cluster (ONC), while 13% of the YSOs are found in a Distributed Population. A lower fraction of protostars in the Distributed Population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups show that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only $\sim 2$ Myr in age. We find the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or by dynamical interactions in dense, clustered regions.
Luca Ducceschi - One of the best experts on this subject based on the ideXlab platform.
-
phrase detectives utilizing collective intelligence for internet scale language resource creation
International Conference on Artificial Intelligence, 2015Co-Authors: Massimo Poesio, Jon Chamberlain, Udo Kruschwitz, Livio Robaldo, Luca DucceschiAbstract:We are witnessing a paradigm shift in human language technology that may well have an impact on the field comparable to the statistical revolution: acquiring large-scale resources by exploiting collective intelligence. An illustration of this approach is Phrase Detectives, an interactive online game-with-a-purpose for creating anaphorically annotated resources that makes use of a highly Distributed Population of contributors with different levels of expertise. The paper gives an overview of all aspects of Phrase Detectives, from the design of the game and the methods used, to the results obtained so far. It furthermore summarises the lessons that have been learnt in developing the game to help other researchers assess and implement the approach.
-
Phrase detectives: Utilizing collective intelligence for internet-scale language resource creation
IJCAI International Joint Conference on Artificial Intelligence, 2015Co-Authors: Massimo Poesio, Jon Chamberlain, Udo Kruschwitz, Livio Robaldo, Luca DucceschiAbstract:We are witnessing a paradigm shift in Human Language Technology (HLT) that may well have an impact on the field comparable to the statistical revolution: acquiring large-scale resources by exploiting collective intelligence. An illustration of this new approach is Phrase Detectives, an interactive online game with a purpose for creating anaphorically annotated resources that makes use of a highly Distributed Population of contributors with different levels of expertise. The purpose of this article is to first of all give an overview of all aspects of Phrase Detectives, from the design of the game and the HLT methods we used to the results we have obtained so far. It furthermore summarizes the lessons that we have learned in developing this game which should help other researchers to design and implement similar games.
Eric E. Mamajek - One of the best experts on this subject based on the ideXlab platform.
-
a Distributed Population of low mass pre main sequence stars near the taurus molecular clouds
arXiv: Astrophysics, 2006Co-Authors: Catherine L. Slesnick, John M. Carpenter, Lynne A. Hillenbrand, Eric E. MamajekAbstract:We present a drift scan survey covering a ~5 deg by 50 deg region toward the southern portion of the Taurus-Auriga molecular cloud. Data taken in the B,R,I filters with the Quest-2 camera on the Palomar 48-inch telescope were combined with 2MASS near-infrared photometry to select candidate young stars. Follow-up optical spectroscopy of 190 candidates led to identification of 42 new low mass pre-main sequence stars with spectral types M4-M8, of which approximately half exhibit surface gravity signatures similar to known Taurus stars while the other half exhibit surface gravity signatures similar to members of the somewhat older Upper Sco, TW Hya and Beta Pic associations. The pre-main sequence stars are spread over ~35 deg, and many are located well outside of previously explored regions. From assessment of the spatial and proper motion distributions, we argue that the new pre-main sequence stars identified far from the clouds cannot have originated from the vicinity of the 1-2 Myr-old subclusters which contain the bulk of the identified Taurus members, but instead represent a newly-identified area of recent star-formation near the clouds.
-
A Distributed Population OF LOW-MASS PRE-MAIN-SEQUENCE STARS NEAR THE TAURUS MOLECULAR CLOUDS
The Astronomical Journal, 2006Co-Authors: Catherine L. Slesnick, John M. Carpenter, Lynne A. Hillenbrand, Eric E. MamajekAbstract:We present a drift-scan survey covering a ~5° × 50° region toward the southern portion of the Taurus-Auriga molecular cloud. Data taken in the B,R,I filters with the Quest-2 camera on the Palomar 48 inch (1.2 m) Samuel Oschin Telescope were combined with Two Micron All Sky Survey near-infrared photometry to select candidate young stars. Follow-up optical spectroscopy of 190 candidates led to the identification of 42 new low-mass pre-main-sequence stars with spectral types M4-M8, of which approximately half exhibit surface gravity signatures similar to known Taurus stars, while the other half exhibit surface gravity signatures similar to members of the somewhat older Upper Scorpius, TW Hya, and β Pic associations. The pre-main-sequence stars are spread over ~35°, and many are located well outside of previously explored regions. From assessment of the spatial and proper-motion distributions, we argue that the new pre-main-sequence stars identified far from the clouds cannot have originated from the vicinity of the 1-2 Myr old subclusters that contain the bulk of the identified Taurus members but instead represent a newly identified area of recent star formation near the clouds.