Query : 2012A&A...539A..64A

2012A&A...539A..64A - Astronomy and Astrophysics, volume 539A, 64-64 (2012/3-1)

X-ray activity and rotation of the young stars in IC 348.


Abstract (from CDS):

The physical origin of the strong magnetic activity in T Tauri stars and its relation to stellar rotation is not yet well-understood. We investigate the relation between the X-ray activity, rotation, and Rossby number for a sample of young stars in the ≃3Myr old cluster IC 348. We use the data of four Chandra observations of IC 348 to derive the X-ray luminosities of the young stars. Basic stellar parameters and rotation rates are collected from the literature. This results in a sample of 82 X-ray detected stars with known rotation periods. We determine the Rossby numbers (i.e. the ratio of rotation period to convective turnover time) of 76 of these stars from stellar structure- and evolution-models for pre-main sequence stars. The young stars in IC 348 show no correlation between X-ray activity and rotation period. For the Rossby numbers, nearly all IC 348 stars are in the saturated regime of the activity-rotation relation defined by main-sequence stars. Searching for possible super-saturation effects, we find a marginal (but statistically in-significant) trend that the stars with the smallest Rossby numbers have slightly lower X-ray activity levels. There are no significant differences in the X-ray activity level for stars of different spectral types and no relation between spectral type and Rossby number is seen. In addition, for stars belonging to different IR-classes, no significant differences are present for the X-ray activity level as well as for their Rossby numbers. We compare the dispersion in the fractional X-ray luminosities of the stars in the saturated rotation regime in IC 348 to that seen in younger and older stellar populations. The scatter seen in the ≃3Myr old IC 348 [σ(log(LX/Lbol))=0.43] is considerably smaller than for the ≃1Myr old Orion nebula cluster [σ(log(LX/Lbol))=0.63], but, at the same time, considerably larger than the dispersion seen in the ≃30Myr old cluster NGC 2547 [σ(log(LX/Lbol))=0.24] and in main-sequence stars. The results of our X-ray analysis of IC 348 show that neither the rotation rates nor the presence/absence of circumstellar disks are of fundamental importance for determining the level of X-ray activity in TTS. Our results suggest that the scatter in the X-ray activity levels for the rapidly rotating members of young clusters decreases with the age of the stellar population. We interpret this as a signature of the changing interior structure of pre-main sequence stars and the consequent changes in the dynamo mechanisms that are responsible for the magnetic field generation.

Abstract Copyright:

Journal keyword(s): circumstellar matter - stars: pre-main sequence - stars: activity - stars: magnetic field

VizieR on-line data: <Available at CDS (J/A+A/539/A64): table2.dat table3.dat>

Status at CDS : All or part of tables of objects could be ingested in SIMBAD with priority 2.

Simbad objects: 4

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Number of rows : 4
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 IC 348 OpC 03 44 31.7 +32 09 32           ~ 1368 1
2 NAME Taurus Complex SFR 04 41.0 +25 52           ~ 4248 0
3 NAME Orion Nebula Cluster OpC 05 35.0 -05 29           ~ 2268 0
4 NGC 2547 OpC 08 09 52.360 -49 10 35.01           ~ 388 0

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