[ { "id": "authors:2kz8e-57x34", "collection": "authors", "collection_id": "2kz8e-57x34", "cite_using_url": "https://authors.library.caltech.edu/records/2kz8e-57x34", "type": "book_section", "title": "A Search for Disk-Locking in the Chamaeleon I Star Forming Region", "author": [ { "family_name": "Nguyen", "given_name": "Duy Cuong" }, { "family_name": "Jayawardhana", "given_name": "Ray", "orcid": "0000-0001-5349-6853", "clpid": "Jayawardhana-Ray" }, { "family_name": "van Kerkwijk", "given_name": "Marten", "orcid": "0000-0002-5830-8505" }, { "family_name": "Brandeker", "given_name": "Alexis", "orcid": "0000-0002-7201-7536" }, { "family_name": "Scholz", "given_name": "Aleks", "orcid": "0000-0001-8993-5053" } ], "abstract": "We investigated the connection between disks and stellar rotation. Disk-locking theory predicts that accreting stars are preferentially slow rotators compared to their peers. If true, classical T Tauri stars (CTTS), which are accreting based on strong Ha emission, should have observably lower v sin i values compared to weak-lined T Tauri stars (WTTS), which are not accreting. We present our findings from high-resolution optical spectra taken with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph on the Magellan Clay 6.5-m telescope located at the Las Campanas Observatory of 63 T Tauri stars in the Cha I SFR.", "doi": "10.1007/978-3-540-75485-5_77", "issn": "1431-2433", "publisher": "Springer Berlin Heidelberg", "publication": "ESO Astrophysics Symposia", "publication_date": "2008", "pages": "307-308" }, { "id": "authors:dwgrm-qe025", "collection": "authors", "collection_id": "dwgrm-qe025", "cite_using_url": "https://authors.library.caltech.edu/records/dwgrm-qe025", "type": "book_section", "title": "Close Companions to Nearby Young Stars from Adaptive Optics Imaging on VLT and Keck", "author": [ { "family_name": "Haisch", "given_name": "Karl E." }, { "family_name": "Jayawardhana", "given_name": "Ray", "orcid": "0000-0001-5349-6853", "clpid": "Jayawardhana-Ray" }, { "family_name": "Brandeker", "given_name": "Alexis", "orcid": "0000-0002-7201-7536" }, { "family_name": "Mardones", "given_name": "Diego", "orcid": "0000-0002-5065-9175" } ], "abstract": "We report the results of VLT and Keck adaptive optics surveys of known members of the \u03b7 Chamaeleontis, MBM 12, and TW Hydrae (TWA) associations to search for close companions. The multiplicity statistics of \u03b7 Cha, MBM 12, and TWA are quite high compared with other clusters and associations, although our errors are large due to small number statistics. We have resolved S18 in MBM 12 and RECX 9 in \u03b7 Cha into triples for the first time. The tight binary TWA 5Aab in the TWA offers the prospect of measuring the dynamical masses of both components as well as an independent distance to the system within a few years. The AO detection of the close companion to the nearby young star \u03c71 Orionis, previously inferred from radial velocity and astrometric observations, has already made it possible to derive the dynamical masses of that system without any astrophysical assumption.", "doi": "10.1007/10828557_29", "issn": "1431-2433", "publisher": "Springer Berlin Heidelberg", "publication": "ESO Astrophysics Symposia", "publication_date": "2005-11-11", "pages": "177-182" }, { "id": "authors:xvhts-whg37", "collection": "authors", "collection_id": "xvhts-whg37", "cite_using_url": "https://authors.library.caltech.edu/records/xvhts-whg37", "type": "book_section", "title": "Observational Clues to Brown Dwarf Origins", "author": [ { "family_name": "Jayawardhana", "given_name": "Ray", "orcid": "0000-0001-5349-6853", "clpid": "Jayawardhana-Ray" }, { "family_name": "Mohanty", "given_name": "Subhanjoy", "orcid": "0000-0002-9896-8313" }, { "family_name": "Basri", "given_name": "Gibor", "orcid": "0000-0001-9820-8464" }, { "family_name": "Ardila", "given_name": "David R.", "orcid": "0000-0002-2564-8116" }, { "family_name": "Stelzer", "given_name": "Beate", "orcid": "0000-0003-4929-5703" }, { "family_name": "Haisch", "given_name": "Karl E." } ], "abstract": "Over the past year, we have conducted a multi-faceted program to investigate the origin and early evolution of brown dwarfs. Using high-resolution Keck optical spectra of \u223c30 objects near and below the substellar boundary in several star-forming regions, we present compelling evidence for a T Tauri-like accretion phase in young brown dwarfs. Our systematic study of infrared L1-band (3.8\u03bcm) disk excess in \u223c50 spectroscopically confirmed young very low mass objects reveal that a significant fraction of brown dwarfs harbor disks at a very young age. Their inner disk lifetimes do not appear to be vastly di erent from those of disks around T Tauristars. Taken together, our findings are consistent with a common origin for most low-mass stars, brown dwarfs and isolated planetary mass objects.", "doi": "10.1007/1-4020-2600-5_30", "publisher": "Springer Netherlands", "publication": "Open Issues in Local Star Formation", "publication_date": "2003", "pages": "251-258" }, { "id": "authors:7xfkz-k5j21", "collection": "authors", "collection_id": "7xfkz-k5j21", "cite_using_url": "https://authors.library.caltech.edu/records/7xfkz-k5j21", "type": "book_section", "title": "Surface Gravity & Mass in Young Brown Dwarfs and Planemos", "author": [ { "family_name": "Mohanty", "given_name": "Subhanjoy", "orcid": "0000-0002-9896-8313" }, { "family_name": "Jayawardhana", "given_name": "Ray", "orcid": "0000-0001-5349-6853", "clpid": "Jayawardhana-Ray" }, { "family_name": "Basri", "given_name": "Gibor", "orcid": "0000-0001-9820-8464" }, { "family_name": "Allard", "given_name": "France", "orcid": "0000-0003-1929-9340" }, { "family_name": "Hauschildt", "given_name": "Peter", "orcid": "0000-0002-8077-5572" }, { "family_name": "Ardila", "given_name": "David", "orcid": "0000-0002-2564-8116" } ], "abstract": "We analyse high-resolution optical spectra of a sample of low-mass, very young, mid-to late M stellar and substellar objects in Upper Scorpius and Taurus. Precise effective temperatures (\u00b1 50K) and surface gravities (\u00b1 0.25 dex) are derived from amulti-feature spectral analysis using TiO, NaI and KI, through comparison with the latest synthetic spectra. Our high-resolution analysis is independent of extinction estimates. Combining our Teff and gravities with distance and photometry information then allows us to derive extinctions, masses, radii and luminosities. We emphasize that our analysis is independent of theoretical evolutionary models. As such, it offers a new way of deriving fundamental parameters for low-mass stellar and substellar objects, and of testing the model evolutionary tracks. We find discrepancies between our results and the theoretical tracks for the coolest, lowest mass targets. Our gravities for these objects are significantly (\u223c 0.75 dex) lower than for hotter ones. This is at odds with the predictions of the evolutionary models, and causes improbably low ages to be derived from the theoretical tracks for the coolest objects. Similarly, our radii and luminosities for the coolest, lowest mass objects are much larger than predicted by the evolutionary models. These results lead us to suggest that significant improvements in the evolutionary models may be necessary for very cool, ultra-low mass objects, perhaps in the treatment of convection and/or initial conditions. We also find two of our coolest targets to be planetary mass objects (\"planemos\"), with mass \u223c 7 MJ. Thus, some late-M PMS objects may be much less massive than current evolutionary models indicate. Equivalently, young planemos may be more luminous than expected. Combined with the detection of planemos by other groups, our results imply that such objects may not be too rare.", "doi": "10.1007/1-4020-2600-5_31", "publisher": "Springer Netherlands", "publication": "Open Issues in Local Star Formation", "publication_date": "2003", "pages": "259-266" } ]