Gaia view of low-mass star formation

Understanding how young stars and their circumstellar disks form and evolve is key to explain how planets form. The evolution of the star and the disk is regulated by different processes, both internal to the system or related to their environment. The former include accretion of material onto the central star, wind emission, and photoevaporation of the disk due to high-energy radiation from the central star. These are best studied spectroscopically, and the distance to the star is a key parameter in all these studies. Here we present new estimates of the distance to a complex of nearby star-forming clouds obtained combining TGAS distances with measurement of extinction on the line of sight. Furthermore, we show how we plan to study the effects of the environment on the evolution of disks with Gaia, using a kinematic modelling code we have developed to model young star-forming regions.Comment: 4 pages, 1 figure. To appear in the Proceedings of IAU Symposium 330: Astrometry and Astrophysics in the Gaia Sk

X-Shooter study of accretion in ρ\rho-Ophiucus: very low-mass stars and brown dwarfs

We present new VLT/X-Shooter optical and NIR spectra of a sample of 17 candidate young low-mass stars and BDs in the rho-Ophiucus cluster. We derived SpT and Av for all the targets, and then we determined their physical parameters. All the objects but one have M*<0.6 Msun, and 8 have mass below or close to the hydrogen-burning limit. Using the intensity of various emission lines present in their spectra, we determined the Lacc and Macc for all the objects. When compared with previous works targeting the same sample, we find that, in general, these objects are not as strongly accreting as previously reported, and we suggest that the reason is our more accurate estimate of the photospheric parameters. We also compare our findings with recent works in other slightly older star-forming regions to investigate possible differences in the accretion properties, but we find that the accretion properties for our targets have the same dependence on the stellar and substellar parameters as in the other regions. This leads us to conclude that we do not find evidence for a different dependence of Macc with M* when comparing low-mass stars and BDs. Moreover, we find a similar small (1 dex) scatter in the Macc-M* relation as in some of our recent works in other star-forming regions, and no significant differences in Macc due to different ages or properties of the regions. The latter result suffers, however, from low statistics and sample selection biases in the current studies. The small scatter in the Macc-M* correlation confirms that Macc in the literature based on uncertain photospheric parameters and single accretion indicators, such as the Ha width, can lead to a scatter that is unphysically large. Our studies show that only broadband spectroscopic surveys coupled with a detailed analysis of the photospheric and accretion properties allows us to properly study the evolution of disk accretion rates.Comment: accepted for publication in Astronomy & Astrophysics. Abstract shortened to fit arXiv constraint

Searching for physics beyond the Standard Model in the decay B+ -> K+K+pi-

The observation potential of the decay B+ -> K+K+pi- with the ATLAS detector at LHC is described in this paper. In the Standard Model this decay mode is highly suppressed, while in models beyond the Standard Model it could be significantly enhanced. To improve the selection of the K+K+pi- final state, a charged hadron identification using Time-over-Threshold measurements in the ATLAS Transition Radiation Tracker was developed and used.Comment: 12 pages, 4 figures, 1 tabl

Dependable Distributed Computing for the International Telecommunication Union Regional Radio Conference RRC06

The International Telecommunication Union (ITU) Regional Radio Conference (RRC06) established in 2006 a new frequency plan for the introduction of digital broadcasting in European, African, Arab, CIS countries and Iran. The preparation of the plan involved complex calculations under short deadline and required dependable and efficient computing capability. The ITU designed and deployed in-situ a dedicated PC farm, in parallel to the European Organization for Nuclear Research (CERN) which provided and supported a system based on the EGEE Grid. The planning cycle at the RRC06 required a periodic execution in the order of 200,000 short jobs, using several hundreds of CPU hours, in a period of less than 12 hours. The nature of the problem required dynamic workload-balancing and low-latency access to the computing resources. We present the strategy and key technical choices that delivered a reliable service to the RRC06

Time-resolved photometry of the young dipper RX~J1604.3-2130A:Unveiling the structure and mass transport through the innermost disk

Context. RX J1604.3-2130A is a young, dipper-type, variable star in the Upper Scorpius association, suspected to have an inclined inner disk, with respect to its face-on outer disk. Aims. We aim to study the eclipses to constrain the inner disk properties. Methods. We used time-resolved photometry from the Rapid Eye Mount telescope and Kepler 2 data to study the multi-wavelength variability, and archival optical and infrared data to track accretion, rotation, and changes in disk structure. Results. The observations reveal details of the structure and matter transport through the inner disk. The eclipses show 5 d quasi-periodicity, with the phase drifting in time and some periods showing increased/decreased eclipse depth and frequency. Dips are consistent with extinction by slightly processed dust grains in an inclined, irregularly-shaped inner disk locked to the star through two relatively stable accretion structures. The grains are located near the dust sublimation radius (similar to 0.06 au) at the corotation radius, and can explain the shadows observed in the outer disk. The total mass (gas and dust) required to produce the eclipses and shadows is a few % of a Ceres mass. Such an amount of mass is accreted/replenished by accretion in days to weeks, which explains the variability from period to period. Spitzer and WISE infrared variability reveal variations in the dust content in the innermost disk on a timescale of a few years, which is consistent with small imbalances (compared to the stellar accretion rate) in the matter transport from the outer to the inner disk. A decrease in the accretion rate is observed at the times of less eclipsing variability and low mid-IR fluxes, confirming this picture. The v sin i = 16 km s(-1) confirms that the star cannot be aligned with the outer disk, but is likely close to equator-on and to be aligned with the inner disk. This anomalous orientation is a challenge for standard theories of protoplanetary disk formation.Science & Technology Facilities Council (STFC): ST/S000399/1. ESO fellowship. European Union (EU): 823 823. German Research Foundation (DFG): FOR 2634/1 TE 1024/1-1. French National Research Agency (ANR): ANR-16-CE31-0013. Alexander von Humboldt Foundation. European Research Council (ERC): 678 194. European Research Council (ERC): 742 095. National Aeronautics & Space Administration (NASA). National Science Foundation (NSF). National Aeronautics & Space Administration (NASA): NNG05GF22G. National Science Foundation (NSF): AST-0909182, AST-1 313 422

An extensive VLT/X-Shooter library of photospheric templates of pre-main sequence stars

Studies of the formation and evolution of young stars and their disks rely on the knowledge of the stellar parameters of the young stars. The derivation of these parameters is commonly based on comparison with photospheric template spectra. Furthermore, chromospheric emission in young active stars impacts the measurement of mass accretion rates, a key quantity to study disk evolution. Here we derive stellar properties of low-mass pre-main sequence stars without disks, which represent ideal photospheric templates for studies of young stars. We also use these spectra to constrain the impact of chromospheric emission on the measurements of mass accretion rates. The spectra in reduced, flux-calibrated, and corrected for telluric absorption form are made available to the community. We derive the spectral type for our targets by analyzing the photospheric molecular features present in their VLT/X-Shooter spectra by means of spectral indices and comparison of the relative strength of photospheric absorption features. We also measure effective temperature, gravity, projected rotational velocity, and radial velocity from our spectra by fitting them with synthetic spectra with the ROTFIT tool. The targets have negligible extinction and spectral type from G5 to M8. We perform synthetic photometry on the spectra to derive the typical colors of young stars in different filters. We measure the luminosity of the emission lines present in the spectra and estimate the noise due to chromospheric emission in the measurements of accretion luminosity in accreting stars. We provide a calibration of the photospheric colors of young PMS stars as a function of their spectral type in a set of standard broad-band optical and near-infrared filters. For stars with masses of ~ 1.5Msun and ages of ~1-5 Myr, the chromospheric noise converts to a limit of measurable mass accretion rates of ~ 3x10^-10 Msun/yr.Comment: Accepted for publication on Astronomy & Astrophysics. The spectra of the photospheric templates will be uploaded to Vizier, but are already available on request. Abstract shortened for arxiv constraints. Language edited versio

An Ipsilateral Subtrochanteric Femoral Neck Fracture In The Presence Of An Established Subcapital Non-Union

In this case we describe a 56 year old lady who suffered an ipsilateral non-union of a subcapital femoral neck fracture and an acute subtrochanetric fracture. She had been listed for a semi-elective Total Hip Replacement after a delayed presentationfollowing the initial subcapital fracture. She subsequently fell again sustaining a subtrochanteric fracture of the same hip prior to her planned operation.nbsp She was admitted for a complex arthroplasty, where a long stemmed revision femoral component was used. This is the first time an extracapsular fracture has been described in the presence of an established non-union of the ipsilateral hip.nbsp In such cases we believe the patient should be treated in the same manner as a periprosthetic hip fracture where there is an unstable stem

X-Shooter spectroscopy of young stellar objects in Lupus. Atmospheric parameters, membership and activity diagnostics

A homogeneous determination of basic stellar parameters of young stellar object (YSO) candidates is needed to confirm their evolutionary stage, membership to star forming regions (SFRs), and to get reliable values of the quantities related to chromospheric activity and accretion. We used the code ROTFIT and synthetic BT-Settl spectra for the determination of the atmospheric parameters (Teff and logg), the veiling, the radial (RV) and projected rotational velocity (vsini), from X-Shooter spectra of 102 YSO candidates in the Lupus SFR. We have shown that 13 candidates can be rejected as Lupus members based on their discrepant RV with respect to Lupus and/or the very low logg values. At least 11 of them are background giants. The spectral subtraction of inactive templates enabled us to measure the line fluxes for several diagnostics of both chromospheric activity and accretion. We found that all Class-III sources have H$\alpha$ fluxes compatible with a pure chromospheric activity, while objects with disks lie mostly above the boundary between chromospheres and accretion. YSOs with transitional disks displays both high and low H$\alpha$ fluxes. We found that the line fluxes per unit surface are tightly correlated with the accretion luminosity ($L_{\rm acc}$) derived from the Balmer continuum excess. This rules out that the relationships between $L_{\rm acc}$ and line luminosities found in previous works are simply due to calibration effects. We also found that the CaII-IRT flux ratio, $F_{8542}/F_{8498}$, is always small, indicating an optically thick emission source. The latter can be identified with the accretion shock near the stellar photosphere. The Balmer decrement reaches instead, for several accretors, high values typical of optically thin emission, suggesting that the Balmer emission originates in different parts of the accretion funnels with a smaller optical depth.Comment: 28 pages, 26 figures, accepted by A&