Ettore Flaccomio

Publications (73) View all

• Article: X-ray variability of PMS stars - Toward an explanation of the different X-ray properties of CTTS and WTTS

  E. Flaccomio, G. Micela, S. Sciortino
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  ABSTRACT: The intense X-ray emission from coronae and accretion shocks in young PMS stars is likely to play an important role in the evolution and dispersal of circumstellar disks. Several aspects of the physics of this X-ray emission remain mysterious, e.g., whether and how much accretion affects coronal emission. We studied the X-ray variability of ~1 Myr old low-mass PMS stars as a function of timescale, stellar rotation, and stellar characteristics, in order to gain insights on the working of PMS coronae, their X-ray emission, and the circumstellar environment in which they are immersed. We have exploited the ~850 ksec long Chandra observation of the Orion Nebula Cluster obtained by the COUP collaboration in Jan. 2003, and statistically analyzed the X-ray lightcurves of low-mass stars in several subsamples. In particular, we characterized the different X-ray behavior of stars with and without circumstellar accretion disks. Accreting stars (Classical T Tauri Stars, CTTSs) are found to be more variable than non accreting ones (Weak-lined T Tauri Stars, WTTSs) at all timescales and in all the X-ray energy bands considered. Variability is seen to increase with time-scale up to ~10 days, i.e. the longest probed. Signatures of rotational modulation are observed for both CTTSs and WTTSs, and most clearly for CTTSs in the soft X-ray band. Lower mass stars are more variable than higher mass ones. We propose that the difference in variability between CTTSs and WTTSs may be explained assuming that the X-ray emission of CTTS is affected by time-variable absorption due circumstellar structures, such as warps in the inner disk and/or accretion streams. This suggestion is appealing because, in the hypothesis that the coronae of CTTSs and WTTSs are similar, it may also explain why CTTSs have lower and more scattered X-ray emission levels with respect to WTTSs.
  10/2012;
• Article: The Gaia-ESO Public Spectroscopic Survey

  G Gilmore, S Randich, M Asplund, J Binney, P Bonifacio, J Drew, S Feltzing, A Ferguson, R Jeffries, G Micela, [......], S Koposov, A Korn, A Lanzafame, E Pancino, E Paunzen, A Recio-Blanco, G Sacco, R Smiljanic, S Van Eck, N Walton
  The Messenger. 03/2012; 147:25-31.
• Source

  Available from: Ettore Flaccomio

  Article: High resolution spectroscopy of Ne II emission from young stellar objects

  G. G. Sacco, E. Flaccomio, I. Pascucci, F. Lahuis, B. Ercolano, J. H. Kastner, G. Micela, B. Stelzer, M. Sterzik
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  ABSTRACT: Constraining the spatial and thermal structure of the gaseous component of circumstellar disks is crucial to understand star and planet formation. Models predict that the [Ne II] line at 12.81 {\mu}m detected in young stellar objects with Spitzer traces disk gas and its response to high energy radiation, but such [Ne II] emission may also originate in shocks within powerful outflows. To distinguish between these potential origins for mid-infrared [Ne II] emission and to constrain disk models, we observed 32 young stellar objects using the high resolution (R~30000) mid-infrared spectrograph VISIR at the VLT. We detected the 12.81 {\mu}m [Ne II] line in 12 objects, tripling the number of detections of this line in young stellar objects with high spatial and spectral resolution spectrographs. We obtain the following main results: a) In Class I objects the [Ne II] emission observed from Spitzer is mainly due to gas at a distance of more than 20-40 AU from the star, where neon is, most likely, ionized by shocks due to protostellar outflows. b) In transition and pre-transition disks, most of the emission is confined to the inner disk, within 20-40 AU from the central star. c) Detailed analysis of line profiles indicates that, in transition and pre-transition disks, the line is slightly blue-shifted (2-12 km s{^-1}) with respect to the stellar velocity, and the line width is directly correlated with the disk inclination, as expected if the emission is due to a disk wind. d) Models of EUV/X-ray irradiated disks reproduce well the observed relation between the line width and the disk inclination, but underestimate the blue-shift of the line.
  12/2011;
• Source

  Available from: Ettore Flaccomio

  Article: X-ray view of IC348 in the light of an updated cluster census

  B. Stelzer, T. Preibisch, F. Alexander, P. Mucciarelli, E. Flaccomio, G. Micela, S. Sciortino
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  ABSTRACT: We study the properties of the coronae of the low-mass stars in the young (~2-3Myr), nearby (~310pc) open cluster IC348 combining X-ray and optical/infrared data. The four existing Chandra observations of IC348 are merged, thus providing a deeper and spatially more complete X-ray view than previous X-ray studies of the cluster. We have compiled a comprehensive catalog of IC348 members taking into account recent updates to the cluster census. Our data collection comprises fundamental stellar parameters, infrared excess indicating the presence of disks, Halpha emission as a tracer of chromospheric emission or accretion and mass accretion rates. We have detected 290 X-ray sources in four merged Chandra exposures, of which 187 are associated with known cluster members. Only four of the X-ray sources are brown dwarfs (spectral type M6 and later). The detection rate is highest for diskless Class III stars and increases with stellar mass. This may be explained with higher X-ray luminosities for higher mass and later evolutionary stage that is evident in the X-ray luminosity functions. In particular, we find that for the lowest examined masses (0.1-0.25 Msun) there is a difference between the X-ray luminosity functions of accreting and non-accreting stars (classified on the basis of their Halpha emission strength) as well as those of disk-bearing and diskless stars (classified on the basis of the slope of the spectral energy distribution). These differences disappear for higher masses. This is related to our finding that the L_x/L_bol ratio is non-constant across the mass/luminosity sequence of IC348 with a decrease towards lower luminosity stars. Our analysis of an analogous stellar sample in the Orion Nebula Cluster suggests that the decline of L_x/L_ bol for young stars at the low-mass end of the stellar sequence is likely universal.
  11/2011;
• Article: YSOVAR II: Mapping YSO Inner Disk Structure in NGC 2264 with Simultaneous Spitzer and CoRoT Time Series Photometry

  J Stauffer, M Morales-Calderon, L Rebull, L Affer, S Alencar, L Allen, D Barrado, J Bouvier, N Calvet, S Carey, [......], H Smith, I Song, A Szentgyorgi, S Terebey, F Vrba, L Wasserman, A Watson, B Whitney, E Winston, K Wood
  Spitzer Proposal. 05/2011;