Browsing by Subject "orion nebula cluster"
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Item The Mass-Radius Relation Of Young Stars. I. Usco 5, An M4.5 Eclipsing Binary In Upper Scorpius Observed By K2(2015-07) Kraus, Adam L.; Cody, Ann Marie; Covey, Kevin R.; Rizzuto, Aaron C.; Mann, Andrew W.; Ireland, Michael J.; Kraus, Adam L.; Rizzuto, Aaron C.; Mann, Andrew W.We present the discovery that UScoCTIO 5, a known spectroscopic binary in the Upper Scorpius star-forming region (P = 34 days, M-tot sin(i) = 0.64M(circle dot)), is an eclipsing system with both primary and secondary eclipses apparent in K2 light curves obtained during Campaign 2. We have simultaneously fit the eclipse profiles from the K2 light curves and the existing RV data to demonstrate that UScoCTIO 5 consists of a pair of nearly identical M4.5 stars with M-A = 0.329 +/- 0.002 M-circle dot, R-A = 0.834 +/- 0.006 R-circle dot, M-B = 0.317 +/- 0.002 M-circle dot, and R-B = 0.810 +/- 0.006 R-circle dot. The radii are broadly consistent with pre-main-sequence ages predicted by stellar evolutionary models, but none agree to within the uncertainties. All models predict systematically incorrect masses at the 25%-50% level for the HR diagram position of these mid-M dwarfs, suggesting significant modifications to mass-dependent outcomes of star and planet formation. The form of the discrepancy for most model sets is not that they predict luminosities that are too low, but rather that they predict temperatures that are too high, suggesting that the models do not fully encompass the physics of energy transport (via convection and/or missing opacities) and/or a miscalibration of the SpT-T-eff scale. The simplest modification to the models (changing T-eff to match observations) would yield an older age for this system, in line with the recently proposed older age of Upper Scorpius (tau similar to 11 Myr).Item Target Selection For The Apache Point Observatory Galactic Evolution Experiment (APOGEE)(2013-10) Zasowski, G.; Johnson, J. A.; Frinchaboy, P. M.; Majewski, S. R.; Nidever, D. L.; Pinto, H. J. R.; Girardi, L.; Andrews, B.; Chojnowski, S. D.; Cudworth, K. M.; Jackson, K.; Munn, J.; Skrutskie, M. F.; Beaton, R. L.; Blake, C. H.; Covey, K.; Deshpande, R.; Epstein, C.; Fabbian, D.; Fleming, S. W.; Hernandez, D. A. G.; Herrero, A.; Mahadevan, S.; Meszaros, S.; Schultheis, M.; Sellgren, K.; Terrien, R.; van Saders, J.; Prieto, C. A.; Bizyaev, D.; Burton, A.; Cunha, K.; da Costa, L. N.; Hasselquist, S.; Hearty, F.; Holtzman, J.; Perez, A. E. G.; Maia, M. A. G.; O'Connell, R. W.; O'Donnell, C.; Pinsonneault, M.; Santiago, B. X.; Schiavon, R. P.; Shetrone, M.; Smith, V.; Wilson, J. C.; Frinchaboy, P. M.; Jackson, K.The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a high-resolution infrared spectroscopic survey spanning all Galactic environments (i.e., bulge, disk, and halo), with the principal goal of constraining dynamical and chemical evolution models of the Milky Way. APOGEE takes advantage of the reduced effects of extinction at infrared wavelengths to observe the inner Galaxy and bulge at an unprecedented level of detail. The survey's broad spatial and wavelength coverage enables users of APOGEE data to address numerous Galactic structure and stellar populations issues. In this paper we describe the APOGEE targeting scheme and document its various target classes to provide the necessary background and reference information to analyze samples of APOGEE data with awareness of the imposed selection criteria and resulting sample properties. APOGEE's primary sample consists of similar to 10(5) red giant stars, selected to minimize observational biases in age and metallicity. We present the methodology and considerations that drive the selection of this sample and evaluate the accuracy, efficiency, and caveats of the selection and sampling algorithms. We also describe additional target classes that contribute to the APOGEE sample, including numerous ancillary science programs, and we outline the targeting data that will be included in the public data releases.Item Target Selection For The Apache Point Observatory Galactic Evolution Experiment (APOGEE)(2013-10) Zasowski, G.; Johnson, J. A.; Frinchaboy, P. M.; Majewski, S. R.; Nidever, D. L.; Pinto, H. J. R.; Girardi, L.; Andrews, B.; Chojnowski, S. D.; Cudworth, K. M.; Jackson, K.; Munn, J.; Skrutskie, M. F.; Beaton, R. L.; Blake, C. H.; Covey, K.; Deshpande, R.; Epstein, C.; Fabbian, D.; Fleming, S. W.; Hernandez, D. A. G.; Herrero, A.; Mahadevan, S.; Meszaros, S.; Schultheis, M.; Sellgren, K.; Terrien, R.; van Saders, J.; Prieto, C. A.; Bizyaev, D.; Burton, A.; Cunha, K.; da Costa, L. N.; Hasselquist, S.; Hearty, F.; Holtzman, J.; Perez, A. E. G.; Maia, M. A. G.; O'Connell, R. W.; O'Donnell, C.; Pinsonneault, M.; Santiago, B. X.; Schiavon, R. P.; Shetrone, M.; Smith, V.; Wilson, J. C.; Frinchaboy, P. M.; Jackson, K.The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a high-resolution infrared spectroscopic survey spanning all Galactic environments (i.e., bulge, disk, and halo), with the principal goal of constraining dynamical and chemical evolution models of the Milky Way. APOGEE takes advantage of the reduced effects of extinction at infrared wavelengths to observe the inner Galaxy and bulge at an unprecedented level of detail. The survey's broad spatial and wavelength coverage enables users of APOGEE data to address numerous Galactic structure and stellar populations issues. In this paper we describe the APOGEE targeting scheme and document its various target classes to provide the necessary background and reference information to analyze samples of APOGEE data with awareness of the imposed selection criteria and resulting sample properties. APOGEE's primary sample consists of similar to 10(5) red giant stars, selected to minimize observational biases in age and metallicity. We present the methodology and considerations that drive the selection of this sample and evaluate the accuracy, efficiency, and caveats of the selection and sampling algorithms. We also describe additional target classes that contribute to the APOGEE sample, including numerous ancillary science programs, and we outline the targeting data that will be included in the public data releases.Item The Taurus Spitzer Survey: New Candidate Taurus Members Selected Using Sensitive Mid-Infrared Photometry(2010-02) Rebull, L. M.; Padgett, D. L.; McCabe, C. E.; Hillenbrand, L. A.; Stapelfeldt, K. R.; Noriega-Crespo, A.; Carey, S. J.; Brooke, T.; Huard, T.; Terebey, S.; Audard, M.; Monin, J. L.; Fukagawa, M.; Gudel, M.; Knapp, G. R.; Menard, Francois; Allen, L. E.; Angione, J. R.; Baldovin-Saavedra, C.; Bouvier, J.; Briggs, K.; Dougados, C.; Evans, Neal J., II; Flagey, N.; Guieu, S.; Grosso, N.; Glauser, A. M.; Harvey, Paul; Hines, D.; Latter, W. B.; Skinner, S. L.; Strom, S.; Tromp, J.; Wolf, Sebastian; Evans, Neal J., II; Harvey, PaulWe report on the properties of pre-main-sequence objects in the Taurus molecular clouds as observed in seven mid-and far-infrared bands with the Spitzer Space Telescope. There are 215 previously identified members of the Taurus star-forming region in our similar to 44 deg(2) map; these members exhibit a range of Spitzer colors that we take to define young stars still surrounded by circumstellar dust (noting that similar to 20% of the bona fide Taurus members exhibit no detectable dust excesses). We looked for new objects in the survey field with similar Spitzer properties, aided by extensive optical, X-ray, and ultraviolet imaging, and found 148 new candidate members of Taurus. We have obtained follow-up spectroscopy for about half the candidate sample, thus far confirming 34 new members, three probable new members, and 10 possible new members, an increase of 15%-20% in Taurus members. Of the objects for which we have spectroscopy, seven are now confirmed extragalactic objects, and one is a background Be star. The remaining 93 candidate objects await additional analysis and/or data to be confirmed or rejected as Taurus members. Most of the new members are Class II M stars and are located along the same cloud filaments as the previously identified Taurus members. Among non-members with Spitzer colors similar to young, dusty stars are evolved Be stars, planetary nebulae, carbon stars, galaxies, and active galactic nuclei.Item The Young Population Of The Chamaeleon II Dark Cloud(2008-06) Spezzi, Loredana; Alcala, Juan M.; Covino, Elvira; Frasca, Antonio; Gandolfi, Davide; Oliveira, Isa; Chapman, Nicholas; Evans, Neal J.; Huard, Tracy L.; Jorgensen, Jes K.; Merin, Bruno; Stapelfeldt, Karl R.; Evans, Neal J.We discuss the results of the optical spectroscopic follow-up of pre-main-sequence (PMS) objects and candidates selected in the Chamaeleon II dark cloud based on data from the Spitzer Legacy survey "From Molecular Cores to Planet Forming Disks" (c2d) and from previous surveys. Our sample includes both objects with infrared excess selected according to c2d criteria and referred to as young stellar objects and other cloud members and candidates selected from complementary optical and near-infrared data. We characterize the sample of objects by deriving their physical parameters. The vast majority of objects have masses M <= 1 M(circle dot) and ages < 6 Myr. Several of the PMS objects and candidates lie very close to or below the hydrogen-burning limit. A first estimate of the slope of the initial mass function in Cha II is consistent with that of other T associations. The star formation efficiency in the cloud (1%-4%) is consistent with our own estimates for Taurus and Lupus, but significantly lower than for Cha I. This might mean that different star formation activities in the Chamaeleon clouds may reflect a different history of star formation. We also find that the Cha II cloud is turning some 8 M(circle dot) into stars every megayear, which is less than the star formation rate in the other c2d clouds. However, the star formation rate is not steady and evidence is found that the star formation in Cha II might have occurred very rapidly. The H alpha emission of the Cha II PMS objects, as well as possible correlations between their stellar and disk properties, is also investigated.