HD 152246 - a new high-mass triple system and its basic properties

Analyses of multi-epoch, high-resolution (R ~ 50.000) optical spectra of the O-type star HD 152246 (O9 IV according to the most recent classification), complemented by a limited number of earlier published radial velocities, led to the finding that the object is a hierarchical triple system, where a close inner pair (Ba-Bb) with a slightly eccentric orbit (e = 0.11) and a period of 6.0049 days revolves in a 470-day highly eccentric orbit (e = 0.865) with another massive and brighter component A. The mass ratio of the inner system must be low since we were unable to find any traces of the secondary spectrum. The mass ratio A/(Ba+Bb) is 0.89. The outer system has recently been resolved using long-baseline interferometry on three occasions. The interferometry confirms the spectroscopic results and specifies elements of the system. Our orbital solutions, including the combined radial-velocity and interferometric solution indicate an orbital inclination of the outer orbit of 112{\deg} and stellar masses of 20.4 and 22.8 solar masses. We also disentangled the spectra of components A and Ba and compare them to synthetic spectra from two independent programmes, TLUSTY and FASTWIND. In either case, the fit was not satisfactory and we postpone a better determination of the system properties for a future study, after obtaining observations during the periastron passage of the outer orbit (the nearest chance being March 2015). For the moment, we can only conclude that component A is an O9 IV star with v*sin(i) = 210 +\- 10 km/s and effective temperature of 33000 +\- 500 K, while component Ba is an O9 V object with v*sin(i) = 65 +/- 3 km/s and T_eff = 33600 +\- 600 K.Comment: 9 pages, 6 figures, accepted for publication in Astronomy and Astrophysic

Ellipsoidal primary of the RS CVn binary zeta And: Investigation using high-resolution spectroscopy and optical interferometry

We have obtained high-resolution spectroscopy, optical interferometry, and long-term broad band photometry of the ellipsoidal primary of the RS CVn-type binary system zeta And. Based on the optical interferometry the apparent limb darkened diameter of zeta And is 2.55 +/- 0.09 mas using a uniform disk fit. The Hipparcos distance and the limb-darkened diameter obtained with a uniform disk fit give stellar radius of 15.9 +/- 0.8 Rsolar, and combined with bolometric luminosity, it implies an effective temperature of 4665 +/- 140 K. The temperature maps obtained from high resolution spectra using Doppler imaging show a strong belt of equatorial spots and hints of a cool polar cap. The equatorial spots show a concentration around the phase 0.75. This spot configuration is reminiscent of the one seen in the earlier published temperature maps of zeta And. Investigation of the Halpha line reveals both prominences and cool clouds in the chromosphere. Long-term photometry spanning 12 years shows hints of a spot activity cycle, which is also implied by the Doppler images, but the cycle length cannot be reliably determined from the current data.Comment: 9 pages, 9 figures, accepted for A&

GCIRS 7, a pulsating M1 supergiant at the Galactic centre. Physical properties and age

The stellar population in the central parsec of the Galaxy is dominated by an old (several Gyr) population, but young, massive stars dominate the luminosity function. We have studied the most luminous of these stars, GCIRS 7, in order to constrain the age of the recent star formation event in the Galactic Centre and to characterise it as an interferometric reference for observations of the Galactic Centre with the instrument GRAVITY, which will equip the Very Large Telescope Interferometer in the near future. We present the first H-band interferometric observations of GCIRS 7, obtained using the PIONIER visitor instrument on the VLTI using the four 8.2-m unit telescopes. In addition, we present unpublished K-band VLTI/AMBER data, build JHKL light-curves based on data spanning 4 decades, and measured the star's effective temperature using SINFONI spectroscopy. GCIRS 7 is marginally resolved at H-band (in 2013: uniform-disk diameter=1.076+/-0.093mas, R=960+/-92Rsun at 8.33+/-0.35kpc). We detect a significant circumstellar contribution at K-band. The star and its environment are variable in brightness and in size. The photospheric H-band variations are well modelled with two periods: P0~470+/-10 days (amplitude ~0.64mag) and long secondary period LSP~2700-2850 days (~1.1mag). As measured from CO equivalent width, =3600+/-195K. The size, periods, luminosity (=-8.44+/-0.22) and effective temperature are consistent with an M1 supergiant with an initial mass of 22.5+/-2.5Msun and an age of 6.5-10Myr (depending on rotation). This age is in remarkable agreement with most estimates for the recent star formation event in the central parsec. Caution should be taken when using this star as an interferometric reference as it is variable in size, is surrounded by a variable circumstellar environment and large convection cells may form on its photosphere.Comment: Accepted for publication in A&A. 10 pages, 12 figure

GG Tau: the fifth element

We aim at unveiling the observational imprint of physical mechanisms that govern planetary formation in young, multiple systems. In particular, we investigate the impact of tidal truncation on the inner circumstellar disks. We observed the emblematic system GG Tau at high-angular resolution: a hierarchical quadruple system composed of low-mass T Tauri binary stars surrounded by a well-studied, massive circumbinary disk in Keplerian rotation. We used the near-IR 4-telescope combiner PIONIER on the VLTI and sparse-aperture-masking techniques on VLT/NaCo to probe this proto-planetary system at sub-AU scales. We report the discovery of a significant closure-phase signal in H and Ks bands that can be reproduced with an additional low-mass companion orbiting GG Tau Ab, at a (projected) separation rho = 31.7 +/- 0.2mas (4.4 au) and PA = 219.6 +/- 0.3deg. This finding offers a simple explanation for several key questions in this system, including the missing-stellar-mass problem and the asymmetry of continuum emission from the inner dust disks observed at millimeter wavelengths. Composed of now five co-eval stars with 0.02 <= Mstar <= 0.7 Msun, the quintuple system GG Tau has become an ideal test case to constrain stellar evolution models at young ages (few 10^6yr).Comment: 5pages, 3 figures, 1 appendix (online material

The (black hole mass)-(color) relations for early- and late-type galaxies: red and blue sequences

[Abridged] Tight correlations between supermassive black hole (SMBH) mass ($M_{\rm BH}$) and the properties of the host galaxy have useful implications for our understanding of the growth of SMBHs and evolution of galaxies. Here, we present newly observed correlations between $M_{\rm BH}$ and the host galaxy total UV$-$ [3.6] color ($\mathcal{C_{\rm UV,tot}}$, Pearson's r = $0.6-0.7$) for a sample of 67 galaxies (20 early-type galaxies and 47 late-type galaxies) with directly measured $M_{\rm BH}$ in the GALEX/S$^{4}$G survey. The colors are carefully measured in a homogeneous manner using the galaxies' FUV, NUV and 3.6 \micron magnitudes and their multi-component structural decompositions in the literature. We find that more massive SMBHs are hosted by (early- and late-type) galaxies with redder colors, but the $M_{\rm BH}- \mathcal{C_{\rm UV,tot}}$ relations for the two morphological types have slopes that differ at $\sim 2 \sigma$ level. Early-type galaxies define a red sequence in the $M_{\rm BH}- \mathcal{C_{\rm UV,tot}}$ diagrams, while late-type galaxies trace a blue sequence. Within the assumption that the specific star formation rate of a galaxy (sSFR) is well traced by $L_{\rm UV}/L_{\rm 3.6}$, it follows that the SMBH masses for late-type galaxies exhibit a steeper dependence on sSFR than those for early-type galaxies. The $M_{\rm BH}- \mathcal{C_{\rm UV,tot}}$ and $M_{\rm BH}-L_{\rm 3.6,tot}$ relations for the sample galaxies reveal a comparable level of vertical scatter in the log $M_{\rm BH}$ direction, roughly $5\%-27\%$ more than the vertical scatter of the $M_{\rm BH}-\sigma$ relation. Our $M_{\rm BH}- \mathcal{C_{\rm UV,tot}}$ relations suggest different channels of SMBH growth for early- and late-type galaxies, consistent with their distinct formation and evolution scenarios.Comment: 27 pages, 8 figures, 6 tables, accepted for publication in Ap

The 2008 outburst in the young stellar system ZCMa: I. Evidence of an enhanced bipolar wind on the AU-scale

Accretion is a fundamental process in star formation. Although the time evolution of accretion remains a matter of debate, observations and modelling studies suggest that episodic outbursts of strong accretion may dominate the formation of the protostar. Observing young stellar objects during these elevated accretion states is crucial to understanding the origin of unsteady accretion. ZCMa is a pre-main-sequence binary system composed of an embedded Herbig Be star, undergoing photometric outbursts, and a FU Orionis star. The Herbig Be component recently underwent its largest optical photometric outburst detected so far. We aim to constrain the origin of this outburst by studying the emission region of the HI Brackett gamma line, a powerful tracer of accretion/ejection processes on the AU-scale in young stars. Using the AMBER/VLTI instrument at spectral resolutions of 1500 and 12 000, we performed spatially and spectrally resolved interferometric observations of the hot gas emitting across the Brackett gamma emission line, during and after the outburst. From the visibilities and differential phases, we derive characteristic sizes for the Brackett gamma emission and spectro-astrometric measurements across the line, with respect to the continuum. We find that the line profile, the astrometric signal, and the visibilities are inconsistent with the signature of either a Keplerian disk or infall of matter. They are, instead, evidence of a bipolar wind, maybe partly seen through a disk hole inside the dust sublimation radius. The disappearance of the Brackett gamma emission line after the outburst suggests that the outburst is related to a period of strong mass loss rather than a change of the extinction along the line of sight. Based on these conclusions, we speculate that the origin of the outburst is an event of enhanced mass accretion, similar to those occuring in EX Ors and FU Ors.Comment: Accepted for publication in Astronomy and Astrophysics Letter

Masses of the components of SB2 binaries observed with Gaia. II. Masses derived from PIONIER interferometric observations for Gaia validation

In anticipation of the Gaia astrometric mission, a sample of spectroscopic binaries is being observed since 2010 with the Sophie spectrograph at the Haute--Provence Observatory. Our aim is to derive the orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy sufficient to finally obtain the masses of the components with relative errors as small as 1 % when combined with Gaia astrometric measurements. In order to validate the masses derived from Gaia, interferometric observations are obtained for three SB2s in our sample with F-K components: HIP 14157, HIP 20601 and HIP 117186. The masses of the six stellar components are derived. Due to its edge-on orientation, HIP 14157 is probably an eclipsing binary. We note that almost all the derived masses are a few percent larger than the expectations from the standard spectral-type-mass calibration and mass-luminosity relation. Our calculation also leads to accurate parallaxes for the three binaries, and the Hipparcos parallaxes are confirmed.Comment: 10 pages, 3 figures, accepted by MNRA

Conception de signaux de référence pour l'évaluation de la qualité perçue des codecs de la parole et du son

Ce travail vise à fournir les signaux de référence représentatifs des nouvelles techniques de codage pour l'évaluation subjective de la qualité de parole codée. La démarche adoptée consiste à caractériser d'un point de vue perceptif les dégradations apportées par les nouveaux codecs, puis à les relier aux techniques de codage afin de pouvoir les recréer artificiellement. La MDS (Multidimensional Scaling ou analyse multidimensionnelle des proximités) non métrique pondérée est utilisée pour générer l'espace perceptif de dégradations de codecs wideband. L'analyse révèle un espace perceptif à quatre dimensions interprétable vis-à-vis des techniques de codage

Back-hopping in Spin-Transfer-Torque switching of perpendicularly magnetized tunnel junctions

We analyse the phenomenon of back-hopping in spin-torque induced switching of the magnetization in perpendicularly magnetized tunnel junctions. The analysis is based on single-shot time-resolved conductance measurements of the pulse-induced back-hopping. Studying several material variants reveals that the back-hopping is a feature of the nominally fixed system of the tunnel junction. The back-hopping is found to proceed by two sequential switching events that lead to a final state P' of conductance close to --but distinct from-- that of the conventional parallel state. The P' state does not exist at remanence. It generally relaxes to the conventional antiparallel state if the current is removed. The P' state involves a switching of the sole spin-polarizing part of the fixed layers. The analysis of literature indicates that back-hopping occurs only when the spin-polarizing layer is too weakly coupled to the rest of the fixed system, which justifies a posteriori the mitigation strategies of back-hopping that were implemented empirically in spin-transfer-torque magnetic random access memories.Comment: submitted to Phys Rev.