Circumstellar Disks in the Outer Galaxy: the Star-Forming Region NGC 1893

It is still debated whether star formation process depends on environment. In particular it is yet unclear whether star formation in the outer Galaxy, where the environmental conditions are, theoretically, less conducive, occurs in the same way as in the inner Galaxy. We investigate the population of NGC1893, a young cluster ~3-4 Myr in the outer part of the Galaxy (galactic radius >11 Kpc), to explore the effects of environmental conditions on star forming regions. We present infrared observations acquired using the IRAC camera onboard the Spitzer Space Telescope and analyze the color-color diagrams to establish the membership of stars with excesses. We also merge this information with that obtained from Chandra ACIS-I observations, to identify the Class III population. We find that the cluster is very rich, with 242 PMS Classical T-Tauri stars and 7 Class 0/I stars. We identify 110 Class III candidate cluster members in the ACIS-I field of view. We estimate a disk fraction for NGC1893 of about 67%, similar to fractions calculated for nearby star forming regions of the same age. Although environmental conditions are unfavorable, star formation can clearly be very successful in the outer Galaxy, allowing creation of a very rich cluster like NGC1893.Comment: 10 pages,7 figures,4 table

X-ray flares on the UV Ceti-type star CC Eridani: a "peculiar" time-evolution of spectral parameters

Context: Weak flares are supposed to be an important heating agent of the outer layers of stellar atmospheres. However, due to instrumental limitations, only large X-ray flares have been studied in detail until now. Aims: We used an XMM-Newton observation of the very active BY-Dra type binary star CC Eri in order to investigate the properties of two flares that are weaker than those typically studied in the literature. Methods: We performed time-resolved spectroscopy of the data taken with the EPIC-PN CCD camera. A multi-temperature model was used to fit the spectra. We inferred the size of the flaring loops using the density-temperature diagram. The loop scaling laws were applied for deriving physical parameters of the flaring plasma. We also estimated the number of loops involved in the observed flares. Results: A large X-ray variability was found. Spectral analysis showed that all the regions in the light curve, including the flare segments, are well-described by a 3-T model with variable emission measures but, surprisingly, with constant temperatures (values of 3, 10 and 22 MK). The analysed flares lasted ~ 3.4 and 7.1 ks, with flux increases of factors 1.5-1.9. They occurred in arcades made of a few tens of similar coronal loops. The size of the flaring loops is much smaller than the distance between the stellar surfaces in the binary system, and even smaller than the radius of each of the stars. The obtained results are consistent with the following ideas: (i) the whole X-ray light curve of CC Eri could be the result of a superposition of multiple low-energy flares, and (ii) stellar flares can be scaled-up versions of solar flares.Comment: 14 pages, 12 figures. Accepted for publication in Astronomy & Astrophysic

Raman spectroscopy study of the interface structure in (CaCuO2)n/(SrTiO3)m superlattices

Raman spectra of CaCuO2/SrTiO3 superlattices show clear spectroscopic marker of two structures formed in CaCuO2 at the interface with SrTiO3. For non-superconducting superlattices, grown in low oxidizing atmosphere, the 425 cm-1 frequency of oxygen vibration in CuO2 planes is the same as for CCO films with infinite layer structure (planar Cu-O coordination). For superconducting superlattices grown in highly oxidizing atmosphere, a 60 cm-1 frequency shift to lower energy occurs. This is ascribed to a change from planar to pyramidal Cu-O coordination because of oxygen incorporation at the interface. Raman spectroscopy proves to be a powerful tool for interface structure investigation

Activity and Rotation in the young cluster h Per

We study the stellar rotation-activity relation in the crucial age at which stars reach the fastest rotation. To this aim we have analyzed data of the young cluster h Per, very rich and compact, located at 2300 pc, that at an age of 13 Myr should be mainly composed of stars that have ended their contraction phase and that have not lost significant angular momentum viamagnetic breaking. To constrain the activity level of h Per members we have analyzed a deep Chandra/ACIS-I observation. Rotational periods of h Per members have been derived by Moraux et al. (2013) in the framework of the MONITOR project (Aigrain et al. 2007; Irwin et al. 2007). In the Chandra observation we have detected 1010 X-ray sources located in the central field of h Persei. Assuming a distance of 2300 pc their X-ray luminosity ranges between 2x10^29 and 6x10^31 erg/s. Among the 1010 x-ray sources ~600 have as optical counterpart candidate members of the cluster with masses ranging down to 0.3 solar mass, and ˜150 have also measured rotational period. For this sample of ˜150 h Per members we have compared X-ray luminosity and rotational periods for different mass ranges. We have found that solar type stars (~1.3 solar mass) show evidence of supersaturation for short periods. This phenomenon is unobserved for lower mass stars

UNA PANORAMICA SULL\u2019ANEMIA SIDEROPENICA NEGLI ATLETI/AN OVERVIEW ON IRON DEFICIENCY ANEMIA IN ATHLETES

Diversi studi in letteratura riportano come la capacit\ue0 prestativa degli atleti di endurance sia fortemente compromessa in seguito all\u2019insorgenza di anemia sideropenica. Questa, infatti, \ue8 una delle pi\uf9 importanti cause di overtraining negli atleti che pratica attivit\ue0 sportive di lunga durata come: la maratona, la marcia, il ciclismo. Tra le diverse cause di anemia ferropriva ricordiamo: una dieta inadeguata a soddisfare le richieste di ferro dell\u2019organismo, una riduzione dell\u2019assorbimento di ferro a livello intestinale e/o un\u2019eccessiva perdita di questo elemento da parte dell\u2019atleta. Il controllo periodico tramite analisi ematochimiche, metaboliche e funzionali potrebbe essere un valido strumento per individuare precocemente il rischio di insorgenza di anemia negli atleti. Una diagnosi precoce di anemia o del rischio di sviluppare questo pericoloso quadro fisiopatologico potrebbe, infatti, aiutare il tecnico e lo staff medico a rimodulare il carico di lavoro e il regime alimentare dell\u2019atleta a rischio.Several studies showed that athletes\u2019 endurance performance is reduced following the onset of iron deficiency anemia. It, indeed, is one of the main causes of overtraining in athletes who play endurance sports, such as marathon, walking race, cycling. Causes of iron deficiency anemia include: inadequate amounts of iron to meet body demands, decreased absorption of iron from gut and/or excessive loss of iron from athlete\u2019s body. Periodic monitoring evaluation process by ematochemical metabolic and functional analysis could be a valid tool to early identify the risk of anemia in athletes. Early diagnosis of anemia or of the risk of developing this dangerous physiopathological phenomenon could help the technical and medical staff modulate the workload and athlete\u2019s diet at risk of anemia

Circumstellar disks in the outer Galaxy: the star-forming region NGC 1893

Context. It is still debated whether star formation process depends on environment. In particular it is yet unclear whether star formation in the outer Galaxy, where the environmental conditions are, theoretically, less conducive, occurs in the same way as in the inner Galaxy. Aims. We investigate the population of NGC 1893, a young cluster (~3-4 Myr) in the outer part of the Galaxy (R_G ≥ 11 kpc), to explore the effects of environmental conditions on star forming regions. Methods. We present infrared observations acquired using the IRAC camera onboard the Spitzer Space Telescope and analyze the color-color diagrams to establish the membership of stars with excesses. We also merge this information with that obtained from Chandra ACIS-I observations, to identify the Class III population. Results. We find that the cluster is very rich, with 242 PMS Classical T Tauri stars and 7 Class 0/I stars. We identify 110 Class III candidate cluster members in the ACIS-I field of view. We estimate a disk fraction for NGC 1893 of about 67%, similar to fractions calculated for nearby star forming regions of the same age. Conclusions. Although environmental conditions are unfavorable, star formation can clearly be very successful in the outer Galaxy, allowing creation of a very rich cluster like NGC 1893

Hard X-ray flux from low-mass stars in the Cygnus OB2 Association

Context. The Cygnus OB2 association, the central engine of the Cygnus X star-forming region, is the subject of an extensive INTEGRAL Key Project that will accumulate 6Ms of observations. Analysis of 2Ms of observations by De Becker and co-workers provides the most sensitive limit yet obtained on hard X-ray emission from the cluster. Aims. We investigate the X-ray emission in the 20-40 keV band expected from the flaring low-mass stellar population in Cygnus OB2. We discuss whether such emission needs to be considered in the interpretation of existing and future X-ray observations of the region, and whether such observations might provide insight into the high-energy processes on low-mass pre-main sequence stars. Methods. The total hard X-ray flux from low-mass stars is estimated by assuming the observed soft X-ray emission stems from a superposition of flares. We further assume the ratio of hard X-ray to soft X-ray emission is described by a scaling found for solar flares by Isola and co-workers. Results. We estimate the low-mass stellar hard X-ray flux in the 20-40 keV band to lie in the range ~2x10^31-6x10^32 erg/s and discuss some potential biases that might affect this result. Conclusions. Hard X-ray emission could lie at a level not much below the current observed flux upper limits for Cygnus OB2. If this emission could be detected, it would provide insight into the hard X-ray production of large flares on pre-main sequence stars. We highlight the penetrating power of hard X-rays from low-mass stellar populations as a possible pointer to our Galaxy's hidden star-forming clusters and super-clusters using more sensitive observations from future missions.Comment: 5 page

The Gaia-ESO Survey: membership and Initial Mass Function of the Gamma Velorum cluster

Understanding the properties of young open clusters, such as the Initial Mass Function (IMF), star formation history and dynamic evolution, is crucial to obtain reliable theoretical predictions of the mechanisms involved in the star formation process. We want to obtain a list, as complete as possible, of confirmed members of the young open cluster Gamma Velorum, with the aim of deriving general cluster properties such as the IMF. We used all available spectroscopic membership indicators within the Gaia-ESO public archive together with literature photometry and X-ray data and, for each method, we derived the most complete list of candidate cluster members. Then, we considered photometry, gravity and radial velocities as necessary conditions to select a subsample of candidates whose membership was confirmed by using the lithium and H$\alpha$ lines and X-rays as youth indicators. We found 242 confirmed and 4 possible cluster members for which we derived masses using very recent stellar evolutionary models. The cluster IMF in the mass range investigated in this study shows a slope of $\alpha=2.6\pm0.5$ for $0.5<M/M_\odot <1.3$ and $\alpha=1.1\pm0.4$ for $0.16<M/M_\odot <0.5$ and is consistent with a standard IMF. The similarity of the IMF of the young population around $\gamma^2$Vel to that in other star forming regions and the field suggests it may have formed through very similar processes.Comment: Accepted for publication in A&A; 18 pages, 11 figures, 5 table

A PC-Based Instrument for Automatic Monitoring and Control of a CPVT Power Plant

A PC-based instrument has been developed for the monitoring and control of a concentrated photovoltaic and thermal (CPVT) power plant. The instrument allows acquiring both electrical and thermal quantities. Moreover it implements the solar tracking algorithm used to optimize the power production