V. Roccatagliata

Publications (7)0 Total impact

• Source

  Available from: Aurora Sicilia-Aguilar

  Article: Star formation and disk properties in Pismis 24

  M. Fang, R. van Boekel, R. R. King, Th. Henning, J. Bouwman, Y. Doi, Y. K. Okamoto, V. Roccatagliata, A. Sicilia-Aguilar
  [show abstract] [hide abstract]
  ABSTRACT: (abridged) We investigate the properties of young stars and their disks in the NGC 6357 complex, concentrating on the most massive star cluster within the complex: Pismis 24. We discover two new young clusters in the NGC 6357 complex. We give a revised distance estimate for Pismis 24 of 1.7+-0.2 kpc. We find that the massive star Pis 24-18 is a binary system, with the secondary being the main X-ray source of the pair. We derive the cluster mass function and find that up to the completeness limit at low masses it agrees well with the IMF of the Trapezium cluster. We derive a median age of 1 Myr for the Pismis 24 cluster members. We find five proplyds in HST archival imaging of the cluster, four of which are newly found. In all cases the proplyd tails are pointing directly away from the massive star system Pis 24-1. One proplyd shows a second tail, pointing away from Pis 24-2, suggesting this object is being photoevaporated from two directions simultaneously. We find that the global disk frequency (~30%) in Pismis 24 is much lower than some other clusters of similar age, such as the Orion Nebula Cluster. When comparing the disk frequencies in 19 clusters/star-forming regions of various ages and different (massive) star content, we find that the disks in clusters harboring extremely massive stars (typically earlier than O5), like Pismis 24, are dissipated roughly twice as quickly as in clusters/star-forming regions without extremely massive stars. Within Pismis 24, we find that the disk frequency within a projected distance of 0.6 pc from Pis 24-1 is substantially lower than at larger radii (~19% vs. ~37%). We argue for a combination of photoevaporation and irradiation with ionizing UV photons from nearby massive stars, causing increased MRI-induced turbulence and associated accretion activity, to play an important role in the dissipation of low-mass star disks in Pismis 24.
  01/2012;
• Source

  Available from: Jeroen Bouwman

  Article: Multi-wavelength observations of the young binary system Haro 6-10: The case of misaligned discs

  V. Roccatagliata, Th. Ratzka, Th. Henning, S Wolf, Ch. Leinert, J. Bouwman
  [show abstract] [hide abstract]
  ABSTRACT: Context. We present a multi-wavelength, high-resolution observational survey of the young binary system Haro 6-10 (GV Tau, IRAS 04263+2426), which is harbouring one of the few known infrared companions. Aims. The primary goal of this project is to determine the physical and geometrical properties of the circumstellar and circumbinary material in the Haro 6-10 system. Methods. High-resolution optical (HST/WFPC2) and near-infrared (VLT/NACO) images in different bands were analysed to investigate the large-scale structures of the material around the binary.Mid-infrared interferometry (VLTI/MIDI) and spectroscopy (TIMMI2 at the 3.6m ESO telescope) were carried out to determine the structure and optical depth of the circumstellar material around the individual components. Results. The multi-wavelength observations suggest that both components of the binary system Haro 6-10 are embedded in a common envelope. The measured extinction indicates a dust composition of the envelope similar to that of the interstellar medium. Each component of the system has a circumstellar disc-like structure typical of young stars. The discs are highly misaligned: the northern component is seen almost edge-on and the southern component is an almost face-on disc. Conclusions. The two main formation scenarios of binary systems with misaligned discs are the gravitational capture of a passing object in a dense environment, and the fragmentation of the collapsing molecular cloud. Given the low-density environment of the Taurus-Aurigae star-forming region, the first scenario is unlikely for Haro 6-10. The binary system most probably formed via fragmentation of two different parts of the collapsing molecular cloud combined with other dynamical processes related to the cloud and/or the protostars. This can be the explanation also for other binary systems with an infrared companion.
  07/2011;
• Article: Planetary companions around the metal-poor star HIP 11952

  J. Setiawan, V. Roccatagliata, D. Fedele, Th. Henning, A. Pasquali, M. V. Rodríguez-Ledesma, E. Caffau, U. Seemann, R. J. Klement
  [show abstract] [hide abstract]
  ABSTRACT: Aims. We carried out a radial-velocity survey to search for planets around metal-poor stars. In this paper we report the discovery of two planets around HIP 11952, a metal-poor star with [Fe/H]= -1.9 that belongs to our target sample. Methods. Radial velocity variations of HIP 11952 were monitored systematically with FEROS at the 2.2 m telescope located at the ESO La Silla observatory from August 2009 until January 2011. We used a cross-correlation technique to measure the stellar radial velocities (RV). Results. We detected a long-period RV variation of 290 d and a short-period one of 6.95 d. The spectroscopic analysis of the stellar activity reveals a stellar rotation period of 4.8 d. The Hipparcos photometry data shows intra-day variabilities, which give evidence for stellar pulsations. Based on our analysis, the observed RV variations are most likely caused by the presence of unseen planetary companions. Assuming a primary mass of 0.83 M\odot, we computed minimum planetary masses of 0.78 MJup for the inner and 2.93 MJup for the outer planet. The semi-major axes are a1 = 0.07 AU and a2 = 0.81 AU, respectively. Conclusions. HIP 11952 is one of very few stars with [Fe/H]< -1.0 which have planetary companions. This discovery is important to understand planet formation around metal-poor stars
  AIP Conference Proceedings 03/2011; 1331:182-189.
• Source

  Available from: Aurora Sicilia-Aguilar

  Article: The Long-Lived Disks in the Eta Chamaeleontis Cluster

  A. Sicilia-Aguilar, J. Bouwman, A. Juhasz, Th. Henning, V. Roccatagliata, W. A. Lawson, B. Acke, E. D. Feigelson, A. G. G. M. Tielens, L. Decin, G. Meeus
  [show abstract] [hide abstract]
  ABSTRACT: We present IRS spectra and revised MIPS photometry for the 18 members of the Eta Chamaeleontis cluster. Aged 8 Myr, the Eta Cha cluster is one of the few nearby regions within the 5-10 Myr age range, during which the disk fraction decreases dramatically and giant planet formation must come to an end. For the 15 low-mass members, we measure a disk fraction ~50%, high for their 8 Myr age, and 4 of the 8 disks lack near-IR excesses, consistent with the empirical definition of "transition'' disks. Most of the disks are comparable to geometrically flat disks. The comparison with regions of different ages suggests that at least some of the "transition" disks may represent the normal type of disk around low-mass stars. Therefore, their flattened structure and inner holes may be related to other factors (initial masses of the disk and the star, environment, binarity), rather than to pure time evolution. We analyze the silicate dust in the disk atmosphere, finding moderate crystalline fractions (~10-30%) and typical grain sizes ~1-3 micron, without any characteristic trend in the composition. These results are common to other regions of different ages, suggesting that the initial grain processing occurs very early in the disk lifetime (<1 Myr). Large grain sizes in the disk atmosphere cannot be used as a proxy for age, but are likely related to higher disk turbulence. The dust mineralogy varies between the 8-12micron and the 20-30 micron features, suggesting high temperature dust processing and little radial mixing. Finally, the analysis of IR and optical data on the B9 star Eta Cha reveals that it is probably surrounded by a young debris disk with a large inner hole, instead of being a classical Be star.
  06/2009;
• Article: The Long-Lived Disks in the Eta Chamaeleontis Cluster

  A. Sicilia-Aguilar, J. Bouwman, A. Juhasz, T. Henning, V. Roccatagliata, Lawson, W.~A, B. Acke, Feigelson, E.~D, Tielens, A.~G.~G.~M, L. Decin, G. Meeus
  ArXiv e-prints. 06/2009;
• Source

  Available from: ArXiv

  Article: Long-wavelength observations of debris discs around sun-like stars

  V. Roccatagliata, Th. Henning, S Wolf, J. Rodmann, S. Corder, J. M. Carpenter, M Meyer, D. Dowell
  [show abstract] [hide abstract]
  ABSTRACT: [Abridged] We present two deep surveys of circumstellar discs around solar-type stars at different ages carried out at 350 micron with the CSO and at 1.2 mm with the IRAM 30-m telescope. The aim of this study is to understand the evolution timescale of circumstellar debris discs, and the physical mechanisms responsible for such evolution around solar-type stars. In addition, we perform a detailed characterisation of the detected debris discs. Theoretically, the mass of the disc is expected to decrease with time. In order to test this hypothesis, we performed the generalised Kendall's tau correlation and three different two-sample tests. A characterisation of the detected debris discs has been obtained by computing the collision and Poynting-Robertson timescales and by modelling the spectral energy distribution. The Kendall's tau correlation yields a probability of 76% that the mass of debris discs and their age are correlated. Similarly, the three two-sample tests give a probability between 70 and 83% that younger and older debris systems belong to different parent populations in terms of dust mass. We detected submillimetre/millimetre emission from six debris discs, enabling a detailed SED modelling. Our results on the correlation and evolution of dust mass as a function of age are conditioned by the sensitivity limit of our survey. Deeper millimetre observations are needed to confirm the evolution of debris material around solar-like stars. In the case of the detected discs, the comparison between collision and Poynting-Robertson timescales supports the hypothesis that these discs are collision dominated. All detected debris disc systems show the inner part evacuated from small micron-sized grains. Comment: Accepted by A&A
  02/2009;
• Article: Long-wavelength observations of debris discs around sun-like stars

  V. Roccatagliata, Th. Henning, S Wolf, J. Rodmann, S. Corder, J. M. Carpenter, M. R. Meyer, D. Dowell
  [show abstract] [hide abstract]
  ABSTRACT: Context. Tracing the evolution of debris discs is essential for our understanding of the architecture of planetary system. Even though the evolution of their inner discs has been recently studied with the Spitzer Space Telescope at mid- to far-infrared wavelengths, the outer discs are best characterised by sensitive millimetre observations. Aims. The goal of our study is to understand the evolution timescale of circumstellar debris discs, and the physical mechanisms responsible for such evolution around solar-type stars. In addition, we make a detailed characterisation of the detected debris discs.Methods. Two deep surveys of circumstellar discs around solar-type stars at different ages were carried out at 350 $\mu$m with the CSO and at 1.2 mm with the IRAM 30-m telescope. The dust disc masses were computed from the millimetre emission, where the discs are optically thin. Theoretically, the mass of the disc is expected to decrease with time. To test this hypothesis, we performed the generalised Kendall's tau correlation and three different two-sample tests. A characterisation of the detected debris discs has been obtained by computing the collision and Poynting-Robertson timescales and by modelling the spectral energy distribution.Results. The Kendall's tau correlation yields a probability of 76% that the mass of debris discs and their age are correlated. Similarly, the three two-sample tests give a probability between 70 and 83% that younger and older debris systems belong to different parent populations in terms of dust mass. We detected submillimetre/millimetre emission from six debris discs, enabling a detailed SED modelling.Conclusions. Our results on the correlation and evolution of dust mass as a function of age are conditioned by the sensitivity limit of our survey. Deeper millimetre observations are needed to confirm the evolution of debris material around solar-like stars. In the case of the detected discs, the comparison between collision and Poynting-Robertson timescales supports the hypothesis that these discs are dominated by collisions. All detected debris disc systems show the inner part evacuated from small micron-sized grains.
  http://dx.doi.org/10.1051/0004-6361/200811018.