| 1. |
- Cuong Nguyen, Duy, et al.
(författare)
-
Disk-Braking in Young Stars : Probing Rotation in Chamaeleon I and Taurus-Auriga
- 2009
-
Annan publikation (populärvet., debatt m.m.)abstract
- We present a comprehensive study of rotation, disk and accretion signatures for 144 T Tauri stars in the young (~2 Myr old) Chamaeleon I and Taurus-Auriga star forming regions based on multi-epoch high-resolution optical spectra from the Magellan Clay 6.5 m telescope supplemented by mid-infared photometry from the Spitzer Space Telescope. In contrast to previous studies in the Orion Nebula Cluster and NGC 2264, we do not see a clear signature of disk braking in Tau-Aur and Cha I. We find that both accretors and non-accretors have similar distributions of v sin i. The rotational velocities in both regions show a clear mass dependence, with F--K stars rotating on average about twice as fast as M stars, consistent with results reported for other clusters of similar age. Similarly, we find the upper envelope of the observed values of specific angular momentum j varies as M^0.5 for our sample which spans a mass range of ~0.16 to ~3 M_sun. This power law complements previous studies in Orion which estimated j is proportional to M^0.25 for < ~2 Myr stars in the same mass regime, and a sharp decline in j with decreasing mass for older stars (~10 Myr) with M < 2 M_sun. For a subsample of 67 objects with mid-IR photometry, we examine the connection between accretion signatures and dusty disks: in the vast majority of cases (63/67), the two properties correlate well, which suggests that the timescale of gas accretion is similar to the lifetime of inner disks.
|
|
| 2. |
- Damjanov, Ivana, et al.
(författare)
-
A Comprehensive View of Circumstellar Disks in Chamaeleon I : Infrared Excess, Accretion Signatures, and Binarity
- 2007
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 670:2, s. 1337-1346
-
Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive study of disks around 81 young, low‐mass stars and brown dwarfs in the nearby 2 Myr old Chamaeleon I star‐forming region. We use mid‐infrared photometry from the Spitzer Space Telescope, supplemented by findings from ground‐based high‐resolution optical spectroscopy and adaptive optics imaging. We derive disk fractions of 52%±6% and 58-7+6% based on 8 and 24 μm color excesses, respectively, consistent with those reported for other clusters of similar age. Within the uncertainties, the disk frequency in our sample of K3–M8 objects in Cha I does not depend on stellar mass. Diskless and disk‐bearing objects have similar spatial distributions. There are no obvious transition disks in our sample, implying a rapid timescale for the inner disk clearing process; however, we find two objects with weak excess at 3–8 μm and substantial excess at 24 μm, which may indicate grain growth and dust settling in the inner disk. For a subsample of 35 objects with high‐resolution spectra, we investigate the connection between accretion signatures and dusty disks: in the vast majority of cases (29/35) the two are well correlated, suggesting that, on average, the timescale for gas dissipation is similar to that for clearing the inner dust disk. The exceptions are six objects for which dust disks appear to persist even though accretion has ceased or dropped below measurable levels. Adaptive optics images of 65 of our targets reveal that 17 have companions at (projected) separations of 10–80 AU. Of the five <20 AU binaries, four lack infrared excess, possibly indicating that a close companion leads to faster disk dispersal. The closest binary with excess is separated by ~20 AU, which sets an upper limit of ~8 AU for the outer disk radius. The overall disk frequency among stars with companions (35-13+15%) is lower than (but still statistically consistent with) the value for the total sample.
|
|
| 3. |
- Nguyen, Duy Cuong, et al.
(författare)
-
Disk Braking in young Stars : Probing Rotation in Chamaeleon i and Taurus-Auriga
- 2009
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 695, s. 1648-1656
-
Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive study of rotation, disk, and accretion signatures for 144 T Tauri stars in the young (~2 Myr old) Chamaeleon I and Taurus-Auriga star-forming regions based on multi-epoch high-resolution optical spectra from the Magellan Clay 6.5 m telescope supplemented by mid-infrared photometry from the Spitzer Space Telescope. In contrast to previous studies in the Orion Nebula Cluster and NGC 2264, we do not see a clear signature of disk braking in Tau-Aur and Cha I. We find that both accretors and non-accretors have similar distributions of vsin i. This result could be due to different initial conditions, insufficient time for disk braking, or a significant age spread within the regions. The rotational velocities in both regions show a clear mass dependence, with F-K stars rotating on average about twice as fast as M stars, consistent with results reported for other clusters of similar age. Similarly, we find the upper envelope of the observed values of specific angular momentum j varies as M 0.5 for our sample which spans a mass range of ~0.16-3 M sun. This power law complements previous studies in Orion which estimated j vprop M 0.25 for lsim2 Myr stars in the same mass regime, and a sharp decline in j with decreasing mass for older stars (~10 Myr) with M < 2 M sun. Furthermore, the overall specific angular momentum of this ~10 Myr population is five times lower than that of non-accretors in our sample, and implies a stellar braking mechanism other than disk braking could be at work. For a subsample of 67 objects with mid-infrared photometry, we examine the connection between accretion signatures and dusty disks: in the vast majority of cases (63/67), the two properties correlate well, which suggests that the timescale of gas accretion is similar to the lifetime of inner disks.
|
|
