UVES spectra of young brown dwarfs in Cha I: radial and rotational velocities

Based on high-resolution UVES spectra we found that the radial velocity (RV) dispersion of nine of twelve known young bona fide and candidate brown dwarfs in the Cha I dark cloud is 2.0 km/s, i.e. significantly smaller than the RV dispersion of T Tauri stars in Cha I (3.6 km/s) and only slightly larger than the dispersion of the surrounding molecular gas (1.2 km/s) (Mizuno et al. 1999). This result indicates that the majority of these brown dwarfs are not ejected with high velocity out of a dense region as proposed by some formation scenarios for brown dwarfs. The mean RV values are consistent with the objects being kinematic members of Cha I. The RV dispersion of the T Tauri stars confined to the Cha I region is based on a compilation of T Tauri stars with known RVs from the literature plus three T Tauri stars observed with UVES and unpublished RVs for nine T Tauri stars. Time-resolved spectroscopy revealed RV variations for five out of nine of the bona fide and candidate brown dwarfs in Cha I, which could be due to orbiting planets or surface features. Furthermore we derived rotational velocities vsin(i) and the Lithium 6708 \AA equivalent width.Comment: A&A Letter, in pres

A multiwavelength radial velocity search for planets around the brown dwarf LP 944-20

The nearby brown dwarf LP 944-20 has been monitored for radial velocity variability at optical and near-infrared wavelengths using the VLT/UVES and the Keck/NIRSPEC spectrographs, respectively. The UVES radial velocity data obtained over 14 nights spanning a baseline of 841 days shows significant variability with an amplitude of 3.5 km s$^{-1}$. The periodogram analysis of the UVES data indicates a possible period between 2.5 hours and 3.7 hours, which is likely due to the rotation of the brown dwarf. However, the NIRSPEC data obtained over 6 nights shows an rms dispersion of only 0.36 km s$^{-1}$ and do not follow the periodic trend. These results indicate that the variability seen with UVES is likely to be due to rotationally modulated inhomogeneous surface features. We suggest that future planet searches around very low-mass stars and brown dwarfs using radial velocities will be better conducted in the near-infrared than in the optical.Comment: accepted by ApJ Letter

The Influence of Solar Flares on the Lower Solar Atmosphere: Evidence from the Na D Absorption Line Measured by GOLF/SOHO

Solar flares presumably have an impact on the deepest layers of the solar atmosphere and yet the observational evidence for such an impact is scarce. Using ten years of measurements of the Na D$_{1}$ and Na D$_2$ Fraunhofer lines, measured by GOLF onboard SOHO, we show that this photospheric line is indeed affected by flares. The effect of individual flares is hidden by solar oscillations, but a statistical analysis based on conditional averaging reveals a clear signature. Although GOLF can only probe one single wavelength at a time, we show that both wings of the Na line can nevertheless be compared. The varying line asymmetry can be interpreted as an upward plasma motion from the lower solar atmosphere during the peak of the flare, followed by a downward motion.Comment: 13 pages, 7 figure

First evidence of pulsations in Vega? Results of today's most extensive spectroscopic search

The impact of rapid rotation on stellar evolution theory remains poorly understood as of today. Vega is a special object in this context as spectroscopic and interferometric studies have shown that it is a rapid rotator seen nearly pole one, a rare orientation particularly interesting for seismic studies. In this paper we present a first systematic search for pulsations in Vega. The goal of the present work is to detect for the first time pulsations in a rapidly rotating star seen nearly pole-on. Vega was monitored in quasi-continuous high-resolution echelle spectroscopy. A total of 4478 spectra were obtained within 3 individual runs in 2008, 2009 and 2010 at high resolution. This data set should represent the most extensive high S/N, high resolution quasi-continuous survey obtained on Vega as of today. Equivalent photospheric absorption profiles were calculated for the stellar spectrum, but also for the telluric lines acting as a radial velocity reference. Residual velocities were analysed and periodic low amplitude variations, potentially indicative of stellar pulsations, detected. All three data sets revealed the presence of residual periodic variations: 5.32 and 9.19 c/d, (A approx 6 m/s) in 2008, 12.71 and 13.25 c/d, (A approx 8 m/s) in 2009 and 5.42 and 10.82 c/d, (A approx 3-4 m/s) in 2010. A Lomb-Scargle periodogram of each velocity bin of the equivalent profile was performed for the 2010 run, not showing the presence of any higher order nrp mode. It is too early to conclude that the variations are due to stellar pulsations, and a confirmation of the detection with a highly stable spectrograph is a necessary next step. If pulsations are confirmed, their very small amplitudes show that the star would belong to a category of very "quiet" pulsators

Subaru high-resolution spectroscopy of Star G in the Tycho supernova remnant

It is widely believed that Type Ia supernovae (SN Ia) originate in binary systems where a white dwarf accretes material from a companion star until its mass approaches the Chandrasekhar mass and carbon is ignited in the white dwarf's core. This scenario predicts that the donor star should survive the supernova explosion, providing an opportunity to understand the progenitors of Type Ia supernovae.In this paper we argue that rotation is a generic signature expected of most non-giant donor stars that is easily measurable. \citep{2004Natur.431.1069R} examined stars in the center of the remnant of SN 1572 (Tycho's SN) and showed evidence that a subgiant star (Star G by their naming convention) near the remnant's centre was the system's donor star. We present high-resolution (R \simeq 40000) spectra taken with the High Dispersion Spectrograph on Subaru of this candidate donor star and measure the star's radial velocity as $79\pm 2$ \kms with respect to the LSR and put an upper limit on the star's rotation of 7.5 \kms. In addition, by comparing images that were taken in 1970 and 2004, we measure the proper motion of Star G to be $\mu_l = -1.6 \pm 2.1$ \masyr and $\mu_b = -2.7 \pm 1.6$ \masyr. We demonstrate that all of the measured properties of Star G presented in this paper are consistent with those of a star in the direction of Tycho's SN that is not associated with the supernova event. However, we discuss an unlikely, but still viable scenario for Star G to be the donor star, and suggest further observations that might be able to confirm or refute it.Comment: Accepted for publication in Ap

Companions of old brown dwarfs, and very low mass stars

Up to now, most planet search projects have concentrated on F to K stars. In order to considerably widen the view, we have stated a survey for planets of old, nearby brown dwarfs and very low mass stars. Using UVES, we have observed 26 brown dwarfs and very low mass stars. These objects are quite inactive and are thus highly suitable for such a project. Two objects were found to be spectroscopic binaries. Another object shows significant radial velocity variations. From our measurements, we conclude that this object either has a planetary-mass companion, or the variations are caused by surface features. Within the errors of the measurements, the remaining objects are constant in radial velocity. While it is impossible to strictly exclude an orbiting planet from sparsely sampled RV data, we conclude that it is unlikely that these objects are orbited by massive planets with periods of 40 days or less.Comment: 7 pages (Latex), 2 figures. accepted for publication in Astronomy & Astrophysic

CORS Baade-Wesselink distance to the LMC NGC 1866 blue populous cluster

We used Optical, Near Infrared photometry and radial velocity data for a sample of 11 Cepheids belonging to the young LMC blue populous cluster NGC 1866 to estimate their radii and distances on the basis of the CORS Baade-Wesselink method. This technique, based on an accurate calibration of the surface brightness as a function of (U-B), (V-K) colors, allows us to estimate, simultaneously, the linear radius and the angular diameter of Cepheid variables, and consequently to derive their distance. A rigorous error estimate on radius and distances was derived by using Monte Carlo simulations. Our analysis gives a distance modulus for NGC 1866 of 18.51+/-0.03 mag, which is in agreement with several independent results.Comment: 21 pages, 10 figures, Accepted for publication in the Astrophysical Journa

Allogenic tissue-specific decellularized scaffolds promote long-term muscle innervation and functional recovery in a surgical diaphragmatic hernia model

Congenital diaphragmatic hernia (CDH) is a neonatal defect in which the diaphragm muscle does not develop properly, thereby raising abdominal organs into the thoracic cavity and impeding lung development and function. Large diaphragmatic defects require correction with prosthetic patches to close the malformation. This treatment leads to a consequent generation of unwelcomed mechanical stress in the repaired diaphragm and hernia recurrences, thereby resulting in high morbidity and significant mortality rates. We proposed a specific diaphragm-derived extracellular matrix (ECM) as a scaffold for the treatment of CDH. To address this strategy, we developed a new surgical CDH mouse model to test the ability of our tissue-specific patch to regenerate damaged diaphragms. Implantation of decellularized diaphragmatic ECM-derived patches demonstrated absence of rejection or hernia recurrence, in contrast to the performance of a commercially available synthetic material. Diaphragm-derived ECM was able to promote the generation of new blood vessels, boost long-term muscle regeneration, and recover host diaphragmatic function. In addition, using a GFP + Schwann cell mouse model, we identified re-innervation of implanted patches. These results demonstrated for the first time that implantation of a tissue-specific biologic scaffold is able to promote a regenerating diaphragm muscle and overcome issues commonly related to the standard use of prosthetic materials

Modeling the Subsurface Structure of Sunspots

While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this paper, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out an helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by \citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic

Generation of a Functioning and Self-Renewing Diaphragmatic Muscle Construct

Surgical repair of large muscular defects requires the use of autologous graft transfer or prosthetic material. Naturally derived matrices are biocompatible materials obtained by tissue decellularization and are commonly used in clinical practice. Despite promising applications described in the literature, the use of acellular matrices to repair large defects has been only partially successful, highlighting the need for more efficient constructs. Scaffold recellularization by means of tissue engineering may improve not only the structure of the matrix, but also its ability to functionally interact with the host. The development of such a complex construct is challenging, due to the complexity of the native organ architecture and the difficulties in recreating the cellular niche with both proliferative and differentiating potential during growth or after damage. In this study, we tested a mouse decellularized diaphragmatic extracellular matrix (ECM) previously described by our group, for the generation of a cellular skeletal muscle construct with functional features. The decellularized matrix was stored using different conditions to mimic the off‐the‐shelf clinical need. Pediatric human muscle precursors were seeded into the decellularized scaffold, demonstrating proliferation and differentiation capability, giving rise to a functioning three‐dimensional skeletal muscle structure. Furthermore, we exposed the engineered construct to cardiotoxin injury and demonstrated its ability to activate a regenerative response in vitro promoting cell self‐renewal and a positive ECM remodeling. Functional reconstruction of an engineered skeletal muscle with maintenance of a stem cell pool makes this a promising tool toward future clinical applications in diaphragmatic regeneratio