TY - JOUR
T1 - X-shooter study of accretion in Chamaeleon I
T2 - II. A steeper increase of accretion with stellar mass for very low-mass stars?
AU - Manara, C. F.
AU - Testi, L.
AU - Herczeg, G. J.
AU - Pascucci, I.
AU - Alcalá, J. M.
AU - Natta, A.
AU - Antoniucci, S.
AU - Fedele, D.
AU - Mulders, G. D.
AU - Henning, T.
AU - Mohanty, S.
AU - Prusti, T.
AU - Rigliaco, E.
N1 - Funding Information:
4 IRAF is distributed by National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.
Funding Information:
Acknowledgements. We thank the anonymous referee for the useful comments that helped improved the presentation of the results. C.F.M. gratefully acknowledges an ESA Research Fellowship and support from the ESO Scientific Visitor Programme. This work was partly supported by the Gothenburg Centre for Advanced Studies in Science and Technology as part of the GoCAS program Origins of Habitable Planets and by the Italian Ministero dell’Istruzione, Università e Ricerca through the grant Progetti Premiali 2012-iALMA (CUP C52I13000140001). I.P. acknowledges support from an NSF Astronomy & Astrophysics Research Grant (ID: 1515392). AN acknowledges funding from Science Foundation Ireland (Grant 13/ERC/I2907). D.F. acknowledges support from the Italian Ministry of Education, Universities and Research project SIR (RBSI14ZRHR). We thank E. Whelan for sharing additional information on ISO-ChaI 127. We acknowledge particularly insightful discussions with C. Clarke. This research made use of Astropy, a community-developed core Python package for Astronomy at http://www.astropy.org, and of the SIM-BAD database, operated at CDS, Strasbourg, France.
Publisher Copyright:
© ESO, 2017.
PY - 2017/8/1
Y1 - 2017/8/1
N2 - The dependence of the mass accretion rate on the stellar properties is a key constraint for star formation and disk evolution studies. Here we present a study of a sample of stars in the Chamaeleon I star-forming region carried out using spectra taken with the ESO VLT/X-shooter spectrograph. The sample is nearly complete down to stellar masses (M∗) ∼0.1 M for the young stars still harboring a disk in this region. We derive the stellar and accretion parameters using a self-consistent method to fit the broadband flux-calibrated medium resolution spectrum. The correlation between accretion luminosity to stellar luminosity, and of mass accretion rate to stellar mass in the logarithmic plane yields slopes of 1.9 ± 0.1 and 2.3 ± 0.3, respectively. These slopes and the accretion rates are consistent with previous results in various star-forming regions and with different theoretical frameworks. However, we find that a broken power-law fit, with a steeper slope for stellar luminosity lower than ∼0.45 L and for stellar masses lower than ∼0.3 M is slightly preferred according to different statistical tests, but the single power-law model is not excluded. The steeper relation for lower mass stars can be interpreted as a faster evolution in the past for accretion in disks around these objects, or as different accretion regimes in different stellar mass ranges. Finally, we find two regions on the mass accretion versus stellar mass plane that are empty of objects: one region at high mass accretion rates and low stellar masses, which is related to the steeper dependence of the two parameters we derived. The second region is located just above the observational limits imposed by chromospheric emission, at M∗ ∼ 0.3-0.4 M. These are typical masses where photoevaporation is known to be effective. The mass accretion rates of this region are ∼10-10M/yr, which is compatible with the value expected for photoevaporation to rapidly dissipate the inner disk.
AB - The dependence of the mass accretion rate on the stellar properties is a key constraint for star formation and disk evolution studies. Here we present a study of a sample of stars in the Chamaeleon I star-forming region carried out using spectra taken with the ESO VLT/X-shooter spectrograph. The sample is nearly complete down to stellar masses (M∗) ∼0.1 M for the young stars still harboring a disk in this region. We derive the stellar and accretion parameters using a self-consistent method to fit the broadband flux-calibrated medium resolution spectrum. The correlation between accretion luminosity to stellar luminosity, and of mass accretion rate to stellar mass in the logarithmic plane yields slopes of 1.9 ± 0.1 and 2.3 ± 0.3, respectively. These slopes and the accretion rates are consistent with previous results in various star-forming regions and with different theoretical frameworks. However, we find that a broken power-law fit, with a steeper slope for stellar luminosity lower than ∼0.45 L and for stellar masses lower than ∼0.3 M is slightly preferred according to different statistical tests, but the single power-law model is not excluded. The steeper relation for lower mass stars can be interpreted as a faster evolution in the past for accretion in disks around these objects, or as different accretion regimes in different stellar mass ranges. Finally, we find two regions on the mass accretion versus stellar mass plane that are empty of objects: one region at high mass accretion rates and low stellar masses, which is related to the steeper dependence of the two parameters we derived. The second region is located just above the observational limits imposed by chromospheric emission, at M∗ ∼ 0.3-0.4 M. These are typical masses where photoevaporation is known to be effective. The mass accretion rates of this region are ∼10-10M/yr, which is compatible with the value expected for photoevaporation to rapidly dissipate the inner disk.
KW - Accretion, accretion disks
KW - Open clusters and associations: individual: Chamaeleon I
KW - Protoplanetary disks
KW - Stars: pre-main sequence
KW - Stars: variables: T Tauri, Herbig Ae/Be
UR - http://www.scopus.com/inward/record.url?scp=85028550397&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/201630147
DO - 10.1051/0004-6361/201630147
M3 - Article
AN - SCOPUS:85028550397
SN - 0004-6361
VL - 604
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A127
ER -