Volume 575, March 2015
|Number of page(s)||17|
|Published online||10 February 2015|
Hβ equivalent widths and fluxes for the members of γ Vel and Cha I observed with UVES.
Mass accretion rates derived in the literature with different methods.
Hartmann et al. (1998) derived mass accretion rates from intermediate-resolution spectrophotometry of the hot continuum emission. Ten accretors are shared with us. Our values and those obtained by these authors agree within the errors with the only exception of J11072825–7652118, for which our Ṁacc is lower than the Hartmann et al. (1998) value by ~1.7 dex, but it is close to the values reported by other authors (see Daemgen et al. 2013). Three accretors of our sample have also been observed by Kim et al. (2009), who measured Ṁacc through U-band photometry. Differences between these values and our determinations are within ~0.3 dex, on average. Recently, Espaillat et al. (2011) have measured Ṁacc with a similar method to the latter authors; for the four accretors in common with, us a mean difference of ~0.5 dex is found. Seven accreting objects are shared with Antoniucci et al. (2011), who measured Ṁacc through the Brγ line. Four stars show similar mass accretion rates, while the values for the three targets with the lowest Ṁacc are higher than ours. Similar differences have also been found by Biazzo et al. (2012) for low-mass stars in Chamaeleon II. Robberto et al. (2012) have derived Ṁacc from Hα photometry for five accretors of our sample. The mean difference in Ṁacc between theirs and our value is ~0.7 dex. Costigan et al. (2012) report Ṁacc measurements using three different diagnostics (EWHα, 10%WHα, and EWCa ii − λ8662) for four accretors in common with us. The agreement between their results and ours is good, especially when we consider the Ṁacc derived from their EWHα. The case of J11075809–7742413 is emblematic because they measure the highest difference in Ṁacc derived through the three methods, but the value obtained with EWHα is very close to ours. This suggests that the discrepancies in the Ṁacc values are mostly due to the method used for deriving it rather than to the different instrumentation used or to an intrinsical variability of the source. Finally, Daemgen et al. (2013) have observed three accretors in common with us and have adopted the Brγ line as diagnostics. The agreement with our values is fairly good, with the exception of 10555973–7724399 for which they have derived log Ṁacc = −7.4 M⊙ yr-1 at odds with our value of −9.1 M⊙ yr-1, which is more similar, within the errors, to the values of −8.8 M⊙ yr-1 and −8.4 M⊙ yr-1 obtained by Robberto et al. (2012) and Hartmann et al. (1998), respectively.
In conclusion, we think that the comparison between our Ṁacc, as derived from the Hα luminosity, and the literature values is in general quite good. The differences/inconsistencies can be attributed to intrinsic short-term and long-term variability (as outlined in Sect. 4.4) and the different photometric/spectroscopic methodologies used by each author to derive accretion luminosity and the mass accretion rate, as well as to the different evolutionary models adopted to estimate the stellar parameters (as also recently pointed out by Alcalá et al. 2014).
Comparison between our Ṁacc values calculated using the EWHα and those obtained by several authors. Dashed and dotted lines represent the one-to-one relation and the position of the typical mean error in Ṁacc of ± 0.5 dex. The legend in the upper left corner explains the meaning of the symbols.
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© ESO, 2015
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