arXiv subjects

Evelyne Alecian

Publications and source records attributed to Evelyne Alecian.

At least 19 recordsLinked to original sources

arXiv2026

Early Exploration of the Scientific Discovery Space for the Habitable Worlds Observatory

The Habitable Worlds Observatory (HWO) is a future NASA flagship mission concept identified by the Astro2020 Decadal Survey as the highest priority for large space missions. HWO should conduct "transformative astrophysics" and search for biosignatures in the atmospheres of approximately 25 potentially Earth-like planets. To further the early-stage development of HWO, NASA formed the Science, Technology, Architecture Review Team (START). In turn, START invited the scientific community to join working groups to explore the potential discovery space. In this paper, we present 70 science cases that resulted from this process. The cases address four scientific pillars: growth of galaxies (15 cases), evolution of the elements (13 cases), solar systems in context (32 cases), and living worlds (10 cases). Combined, they would address 27 of the 30 science questions and discovery areas identified by Astro2020. The 140 observing programs needed for the 70 investigations encompass a rich variety of spectroscopic (for 87% of science cases) and photometric (for 30%) observations extending from the UV to the NIR. Additionally, high-contrast and polarimetric capabilities would be needed for 34% and 27% of science cases, respectively. Access to UV wavelengths is critical: 83% of science cases need data at wavelengths <400 nm, and 26% extend to <100 nm. In the NIR, 26% of science cases need observations at wavelengths >=2000 nm. Pursuing the full portfolio of science would also necessitate precise astrometry for planet mass measurement, rapid response capabilities, a large instantaneous field of regard, non-sidereal tracking, saturation mitigation strategies, and high dynamic range.

astro-ph.IM↗

arXiv2026

Exploring the radial velocity variations of RY Lup with VLT/ESPRESSO: Binary versus spot hypotheses

Stellar multiplicity is a possible cause for creating protoplanetary disc substructures, as tidal forces from a close-in spectroscopic companion can carve out gaps and shape disc architecture. However, in young, active systems, the radial velocity (RV) signatures are often complicated by stellar activity. We investigate RY Lup, a classical T Tauri star hosting a disc with a ~60 au cavity, where studies with Gaia astrometry and VLT/SPHERE imaging hinted at an unseen companion. Using high-resolution VLT/ESPRESSO spectra and the least-squares deconvolution (LSD) technique, we analyse RV variations over 327 days. We detect significant line profile variations with a periodic signal of ~3.75 days, aligning with prior photometric estimates. The variations are compatible with a close-in binary system at ~0.04 au and a mass ratio of q ~ 0.6. Combined analysis of RV data and ALMA dynamical mass estimates, using 13CO and 18CO, reveals a highly misaligned system. The nearly face-on binary i ~ 13 deg is misaligned to both the inner and outer discs i ~ 50 deg and ~70 deg, respectively. The derived orbital separation is compatible with the inner disc size, with the inner rim at a = 0.12 au, measured from VLTI/GRAVITY, which suggests a highly warped disc structure. Nonetheless, the short orbital period conflicts with the derived eccentricity (e ~ 0.23). To explore alternative explanations, we assess the impact of stellar spots on RV signals. While the LSD deformations can be modelled by different cool spot configurations, a 15% dispersion in retrieved v sin i values -- coupled with the lack of a significant periodic signal -- suggests that spots alone cannot explain the observed variability. As neither hypothesis is ruled out, we recommend future combined RV and interferometric monitoring to clarify the nature of the spectroscopic variability.

astro-ph.EP↗

arXiv2026

ExoplaNeT accRetion mOnitoring sPectroscopic surveY (ENTROPY) III. Optical He I line profiles of the accreting super Jupiter Delorme 1 (AB)b

High-resolution spectroscopic observations of helium emission lines provide a powerful probe of accretion geometry in classical T Tauri stars, revealing regions not well traced by hydrogen lines. Parallel studies in the planetary-mass regime are lacking. In this work, we investigate helium emission from the nearby (47 pc), wide-orbit (~84 au), ~13 $M_{Jup}$ accreting circumbinary companion Delorme 1 (AB)b and use resolved line profiles to constrain their origin. We analyse 33 high-S/N VLT/UVES spectra spanning near-ultraviolet to optical wavelengths at R~50,000. We detect seven He I lines at >5$σ$ confidence - 3890, 4027, 4473, 4923, 5017, 5877, and 6680 Ȧ - with significant epoch-to-epoch variability. The He I 5877, 4923, 4473, and 4027 Ȧ lines are asymmetric, showing a narrow component near 0 km/s and a broad component redshifted by ~15 km/s. The accretion luminosity ($1.3^{+1.6}_{-0.7}\times 10^{-5} L_{\odot}$) and mass accretion rate ($0.7^{+0.9}_{-0.4} \times 10^{-8} M_{Jup} yr^{-1}$) inferred from the median He I line luminosities are broadly consistent with, but slightly higher than, estimates from the ultraviolet excess. We conclude that protoplanet Delorme 1 (AB)b shows asymmetric He I profiles analogous to those of classical T Tauri stars, but with much smaller narrow- and broad-component widths. The triplet-singlet line ratio, a strong correlation with ultraviolet excess and the near-zero, redshifted velocities obtained for the narrow component suggest that it originates within the post-shock region, close to the planet surface. The persistent redshift of the broad component, its line width, and velocity correlation with the narrow component imply an origin within the shock structure, closer to the shock front. Emission seems to be dominated by accretion based on the obtained accretion luminosities, but a contribution from chromospheric activity may be present.

astro-ph.EP↗

arXiv2025

ExoplaNeT accRetion mOnitoring sPectroscopic surveY (ENTROPY) - II. Time series of Balmer line profiles of Delorme 1(AB)b

Accretion processes in the planetary-mass regime remain poorly constrained, yet they strongly influence planet formation, evolution, and the composition of circumplanetary disks (CPDs). We investigate the resolved Balmer hydrogen emission-line profiles and their variability in the ~13Mjup, 30-45 Myr-old companion Delorme to constrain the underlying accretion mechanisms. Using VLT/UVES, we obtained 31 new epochs of high-resolution optical spectra (330-680 nm, R = 50,000), probing variability from hours to years. We analyze the shape and flux variability of hydrogen emission lines and compare them to two proposed origins: magnetospheric accretion funnels and localized accretion shocks. We detect Balmer lines from Halpha to H10 (6564-3799 AA) and a UV continuum excess, both indicative of ongoing accretion. All features are variable. The hydrogen lines decompose into two static components that vary only in flux. The broader velocity component correlates strongly with the UV excess and is qualitatively consistent with magnetospheric funnel models, but not with shock models. This component dominates the shape variability. The narrower component, which correlates less with the UV excess, is better matched by shock-emission models and drives most of the flux variability. Line fluxes show low variability on hour timescales but up to ~100% over weeks, similar to T Tauri stars. Our findings support magnetospheric accretion as the origin of the broad component. The narrow component may arise from accretion shocks or chromospheric activity. Higher-cadence observations could reveal rotational modulations and help constrain the object's rotation period and accretion geometry.

astro-ph.EP↗

arXiv2025

GPI+SPHERE detection of a 6.1 $M_{\text{Jup}}$ circumbinary planet around HD 143811

Owing to its sensitivity to wide-orbit giant exoplanets, direct imaging is uniquely positioned to shed light on the interplay between protoplanetary disks and stellar hosts. In addition to constraining formation models, new detections are natural benchmarks for an atmospheric characterization. The COBREX project performed an extensive reanalysis of archival observations from SPHERE and GPI using advanced post-processing techniques, that enhanced the detection sensitivity at close separation. Newly found companion candidates are being followed up to confirm new planets. Following the detection of a companion candidate around the young ($\sim 15$ Myr) binary star HD 143811, we collected a new observation with SPHERE@VLT (0.95-1.67 $μ$m) to confirm the presence of the source and to assess its physical bond to the target. We report the discovery of a new exoplanet orbiting HD 143811 at a projected separation of 0.43" $\sim 60$ au. Based on a 9-year-long baseline, we derive a mostly face-on and low-eccentricity orbit with a period of $320 ^{+250}_{-90}$ years. The luminosity of the planet, constrained through the H-band spectrum from GPI, H-band photometry from SPHERE/IRDIS and YJ upper limits from SPHERE/IFS, allows us to place strong constraints on the intrinsic temperature of the planet (T$_{\text{int}} = 1000 \pm 30$K), which corresponds to a mass of $6.1^{+0.7}_{-0.9} ~M_{\text{Jup}}$. HD 143811(AB)b is the second planet ever discovered by GPI. It joins the small cohort of circumbinary planets discovered through imaging and becomes a prime target for follow-up formation, dynamical, and characterization studies.

astro-ph.EP↗

arXiv2025

Short- and long-term variations of the high mass accretion rate classical T Tauri star DR Tau

Classical T Tauri stars are newly formed, low mass stars which may display both periodic and random variations in their brightness. The interaction between the star and its circumstellar disk is time-dependent, leading to short or long-term changes in the environment, and hence variability of the system. By compiling a large dataset with high-cadence photometric (Kepler, TESS), and high-resolution spectroscopic observations (CFHT/ESPaDOnS) of the highly variable T Tauri star DR Tau, we aim to examine the short- and long-term variability of the system, and identify the underlying physical mechanisms. Our results reveal that DR Tau exhibits stochastic photometric variability not only on daily, but also on hourly timescale with peak-to-peak amplitude of 1.4 mag probably originating from accretion related variations. Our ground-based multifilter photometry shows that the amplitude of the variability decreases with increasing wavelength. This trend towards the infrared wavelengths suggests that part of the disk may be optically thick and invariable. The spectroscopic analysis showed that the H$α$ line presents the most complex line profile with several components but the significance of the components changes over time. This suggests the presence and variation of both accretion flow and wind. Broad and narrow components can be clearly distinguished in the He I and the Ca II lines, suggesting contribution from both the accretion flow and the post-shock region. DR Tau exhibits high level of photometric and spectroscopic variability on both short- and long-timescales, which is caused by the combination of accretion, wind, stellar activity, and obscuration by circumstellar matter; and the significance of the physical mechanisms causing the observed variability changes over time.

astro-ph.SR↗

arXiv2024

Unraveling the binary nature of HQ Tau: A brown dwarf companion revealed using multi-variate Gaussian process

Context. Both the stellar activity and the accretion processes of young stellar objects can induce variations in their radial velocity (RV). This variation is often modulated on the stellar rotation period and may hide a RV signal from a planetary or even a stellar companion. Aims. The aim of this study is to detect the companion of HQ Tau, the existence of which is suspected based on our previous study of this object. We also aim to derive the orbital elements of the system. Methods. We used multi-variate Gaussian process regression on the RV and the bisector inverse slope of a six-month high-resolution spectroscopic follow-up observation of the system to model the stellar activity. This allowed us to extract the Keplerian RV modulation induced by the suspected companion. Results. Our analysis yields the detection of a $\sim$50 M$_{\rm jup}$ brown dwarf companion orbiting HQ Tau with a $\sim$126 day orbital period. Although this is consistent with the modulation seen on this dataset, it does not fit the measurements from our previous work three years earlier. In order to include these measurements in our analysis, we hypothesise the presence of a third component with orbital elements that are consistent with those of the secondary according to our previous analysis (M$_{\rm B}$ $\sim$48 M$_{\rm jup}$, P$_{\rm orb,B}$ $\sim$126 days), and a $\sim$465 M$_{\rm jup}$ tertiary with a $\sim$767 day orbital period. However, the hypothesis of a single companion with M$_{\rm B}$ $\sim$188 M$_{\rm jup}$ and P$_{\rm orb}$ $\sim$247 days can fit both datasets and cannot be completely excluded at this stage of the analysis. Conclusions. At minima, HQ Tau is a single-lined spectroscopic binary, and several factors indicate that the companion is a brown dwarf and that a third component is responsible for larger RV variation on a longer timescale.

astro-ph.SR↗

arXiv2023

Discovery of Magnetospheric Interactions in the Doubly-Magnetic Hot Binary $ε$ Lupi

Magnetic fields are extremely rare in close, hot binaries, with only 1.5\% of such systems known to contain a magnetic star. The eccentric $ε$ Lupi system stands out in this population as the only close binary in which both stars are known to be magnetic. We report the discovery of strong, variable radio emission from $ε$ Lupi using the upgraded Giant Metrewave Radio Telescope (uGMRT) and the MeerKAT radio telescope.The light curve exhibits striking, unique characteristics including sharp, high-amplitude pulses that repeat with the orbital period, with the brightest enhancement occurring near periastron. The characteristics of the light curve point to variable levels of magnetic reconnection throughout the orbital cycle, making $ε$ Lupi the first known high-mass, main sequence binary embedded in an interacting magnetosphere. We also present a previously unreported enhancement in the X-ray light curve obtained from archival XMM-Newton data. The stability of the components' fossil magnetic fields, the firm characterization of their relatively simple configurations, and the short orbital period of the system make $ε$ Lupi an ideal target to study the physics of magnetospheric interactions. This system may thus help us to illuminate the exotic plasma physics of other magnetically interacting systems such as moon-planet, planet-star, and star-star systems including T Tauri binaries, RS CVn systems, and neutron star binaries.

astro-ph.SR↗

arXiv2021

Beyond the dips of V807 Tau, a spectropolarimetric study of a dipper s magnetosphere

We aim to characterize the magnetospheric accretion process in the young stellar object V807 Tau, one of the most stable dippers revealed by K2 in the Taurus star forming region. We performed photometric and spectropolarimetric follow-up observations of this system with CFHT/ESPaDOnS in order to investigate its variability over several rotational periods. We derive a 4.38 day period from the K2 light curve. This period is also seen in the radial velocity variations, ascribed to spot modulation. The narrow component of the He I 5876 Å line as well as the red wing of the Hβ and Hγ line profiles also vary in intensity with the same periodicity. The former traces the accretion shock at the stellar surface, and the latter is a signature of an accretion funnel flow crossing the line of sight. We derive a surface brightness and magnetic field topology from the modeling of Stokes I and V profiles, respectively, for photospheric lines and for the He I line. This reveals a bright spot at the stellar surface, located at a latitude of 60 deg, and a maximum field strength of about 2 kG. The magnetic field topology at the stellar surface is dominated by a dipolar component inclined by about 40 deg onto the spin axis. Despite of its clear and stable dipper behavior, we derive a relatively low inclination of about 50 deg for this system, which calls question the origin of the dips. This low inclination is also consistent with the absence of deep inverse P Cygni components in the line profiles. We conclude that magnetospheric accretion is ongoing in V807 Tau, taking place through non-axisymmetric accretion funnel flows controlled by a strong, tilted, and mainly dipolar magnetic topology. Whether an inner disk warp resulting from this process can account for the dipper character of this source remains to be seen, given the low inclination of the system.

astro-ph.SR↗

arXiv2021

Discovery of eight 'Main-sequence Radio Pulse emitters' using the GMRT: clues to the onset of coherent radio emission in hot magnetic stars

'Main-sequence radio pulse-emitters' (MRPs) are magnetic early-type stars from which periodic radio pulses, produced via electron cyclotron maser emission (ECME), are observed. Despite the fact that these stars can naturally offer suitable conditions for triggering ECME, only seven such stars have been reported so far within a span of more than two decades. In this paper, we report the discovery of eight more MRPs, thus more than doubling the sample size of such objects. These discoveries are the result of our sub-GHz observation program using the Giant Metrewave Radio Telescope over the years 2015-2021. Adding these stars to the previously known MRPs, we infer that at least 32 percent of the magnetic hot stars exhibit this phenomenon, thus suggesting that observation of ECME is not a rare phenomenon. The significantly larger sample of MRPs allows us for the first time to perform a statistical analysis comparing their physical properties. We present an empirical relation that can be used to predict whether a magnetic hot star is likely to produce ECME. Our preliminary analysis suggests that the physical parameters that play the primary role in the efficiency of the phenomenon are the maximum surface magnetic field strength and the surface temperature. In addition, we present strong evidence of the influence of the plasma density distribution on ECME pulse profiles. Results of this kind further motivate the search for MRPs as a robust characterization of the relation between observed ECME properties and stellar physical parameters can only be achieved with a large sample.

astro-ph.SR↗

arXiv2020

The large-scale magnetic field of the eccentric pre-main-sequence binary system V1878 Ori

We report time-resolved, high-resolution optical spectropolarimetric observations of the young double-lined spectroscopic binary V1878 Ori. Our observations were collected with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope through the BinaMIcS large programme. V1878 Ori A and B are partially convective intermediate mass weak-line T Tauri stars on an eccentric and asynchronous orbit. We also acquired X-ray observations at periastron and outside periastron. Using the least-squares deconvolution technique (LSD) to combine information from many spectral lines, we clearly detected circular polarization signals in both components throughout the orbit. We refined the orbital solution for the system and obtained disentangled spectra for the primary and secondary components. The disentangled spectra were then employed to determine atmospheric parameters of the two components using spectrum synthesis. Applying our Zeeman Doppler imaging code to composite Stokes $IV$ LSD profiles, we reconstructed brightness maps and the global magnetic field topologies of the two components. We find that V1878 Ori A and B have strikingly different global magnetic field topologies and mean field strengths. The global magnetic field of the primary is predominantly poloidal and non-axisymmetric (with a mean field strength of 180 G). while the secondary has a mostly toroidal and axisymmetric global field (mean strength of 310 G). These findings confirm that stars with very similar parameters can exhibit radically different global magnetic field characteristics. The analysis of the X-ray data shows no sign of enhanced activity at periastron, suggesting the lack of strong magnetospheric interaction at this epoch.

astro-ph.SR↗

arXiv2019

Fossil field decay due to nonlinear tides in massive binaries

Surface magnetic fields have been detected in 5 to 10% of isolated massive stars, hosting outer radiative envelopes. They are often thought to have a fossil origin, resulting from the stellar formation phase. Yet, magnetic massive stars are scarcer in (close) short-period binaries, as reported by the BinaMIcS (Binarity and Magnetic Interaction in various classes of Stars) collaboration. Different physical conditions in the molecular clouds giving birth to isolated stars and binaries are commonly invoked. In addition, we propose that the observed lower magnetic incidence in close binaries may be due to nonlinear tides. Indeed, close binaries are probably prone to tidal instability, a fluid instability growing upon the equilibrium tidal flow via nonlinear effects. Yet, stratified effects have hitherto been largely overlooked. We theoretically and numerically investigate tidal instability in rapidly rotating, stably stratified fluids permeated by magnetic fields. We use the short-wavelength stability method to propose a comprehensive (local) theory of tidal instability at the linear onset, discussing damping effects. Then, we propose a mixing-length theory for the mixing generated by tidal instability in the nonlinear regime. We successfully assess our theoretical predictions against proof-of-concept, direct numerical simulations. Finally, we compare our predictions with the observations of short-period, double-lined spectroscopic binary systems. Using new analytical results, cross-validated by a direct integration of the stability equations, we show that tidal instability can be generated by nonlinear couplings of inertia-gravity waves with the equilibrium tidal flow in short-period massive binaries, even against the Joule diffusion. In the nonlinear regime, a fossil magnetic field can be dissipated by the turbulent magnetic diffusion induced by the saturated tidal flows. We predict that the turbulent Joule diffusion of fossil fields would occur in a few million years for several short-period massive binaries. Therefore, turbulent tidal flows could explain the observed dearth of some short-period magnetic binaries.

astro-ph.SR↗

arXiv2018

The magnetic fields of intermediate-mass T Tauri stars : I. Magnetic detections and fundamental stellar parameters

Context. The origin of the fossil magnetic fields detected in 5 to 10% of intermediate-mass main sequence stars is still highly debated. Aims. We want to bring observational constraints to a large population of intermediate-mass pre-main sequence (PMS) stars in order to test the theory that convective-dynamo fields generated during the PMS phases of stellar evolution can occasionally relax into fossil fields on the main sequence. Methods. Using distance estimations, photometric measurements, and spectropolarimetric data from HARPSpol and ESPaDOnS of 38 intermediate-mass PMS stars, we determined fundamental stellar parameters (Teff, L and v sin i) and measured surface magnetic field characteristics (including detection limits for non-detections, and longitudinal fields and basic topologies for positive detections). Using PMS evolutionary models, we determined the mass, radius, and internal structure of these stars. We compared different PMS models to check that our determinations were not model-dependant. We then compared the magnetic characteristics of our sample accounting for their stellar parameters and internal structures. Results. We detect magnetic fields in about half of our sample. About 90% of the magnetic stars have outer convective envelopes larger than ~25% of the stellar radii, and heavier than ~2% of the stellar mass. Going to higher mass, we find that the magnetic incidence in intermediate-mass stars drops very quickly, within a time-scale of the order of few times 0.1 Myr. Finally, we propose that intermediate-mass T Tauri stars with large convective envelopes, close to the fully convective limit, have complex fields and that their dipole component strengths may decrease as the sizes of their convective envelopes decrease, similar to lower-mass T Tauri stars.

astro-ph.SR↗

arXiv2016

HD 35502: a hierarchical triple system with a magnetic B5IVpe primary

We present our analysis of HD~35502 based on high- and medium-resolution spectropolarimetric observations. Our results indicate that the magnetic B5IVsnp star is the primary component of a spectroscopic triple system and that it has an effective temperature of $18.4\pm0.6\,{\rm kK}$, a mass of $5.7\pm0.6\,M_\odot$, and a polar radius of $3.0^{+1.1}_{-0.5}\,R_\odot$. The two secondary components are found to be essentially identical A-type stars for which we derive effective temperatures ($8.9\pm0.3\,{\rm kK}$), masses ($2.1\pm0.2\,M_\odot$), and radii ($2.1\pm0.4\,R_\odot$). We infer a hierarchical orbital configuration for the system in which the secondary components form a tight binary with an orbital period of $5.66866(6)\,{\rm d}$ that orbits the primary component with a period of over $40\,{\rm yrs}$. Least-Squares Deconvolution (LSD) profiles reveal Zeeman signatures in Stokes $V$ indicative of a longitudinal magnetic field produced by the B star ranging from approximately $-4$ to $0\,{\rm kG}$ with a median uncertainty of $0.4\,{\rm kG}$. These measurements, along with the line variability produced by strong emission in H$α$, are used to derive a rotational period of $0.853807(3)\,{\rm d}$. We find that the measured $v\sin{i}=75\pm5\,{\rm km\,s}^{-1}$ of the B star then implies an inclination angle of the star's rotation axis to the line of sight of $24^{+6}_{-10}\degree$. Assuming the Oblique Rotator Model, we derive the magnetic field strength of the B star's dipolar component ($14^{+9}_{-3}\,{\rm kG}$) and its obliquity ($63\pm13\degree$). Furthermore, we demonstrate that the calculated Alfvén radius ($41^{+17}_{-6}\,R_\ast$) and Kepler radius ($2.1^{+0.4}_{-0.7}\,R_\ast$) place HD~35502's central B star well within the regime of centrifugal magnetosphere-hosting stars.

astro-ph.SR↗

arXiv2015

A spectro-polarimetric study of the planet-hosting G dwarf, HD 147513

The results from a spectro-polarimetric study of the planet-hosting Sun-like star, HD 147513 (G5V), are presented here. Robust detections of Zeeman signatures at all observed epochs indicate a surface magnetic field, with longitudinal magnetic field strengths varying between 1.0-3.2 G. Radial velocity variations from night to night modulate on a similar timescale to the longitudinal magnetic field measurements. These variations are therefore likely due to the rotational modulation of stellar active regions rather than the much longer timescale of the planetary orbit (Porb=528 d). Both the longitudinal magnetic field measurements and radial velocity variations are consistent with a rotation period of 10 +/- 2 days, which are also consistent with the measured chromospheric activity level of the star (log R'(HK)=-4.64). Together, these quantities indicate a low inclination angle, i~18 degrees. We present preliminary magnetic field maps of the star based on the above period and find a simple poloidal large-scale field. Chemical analyses of the star have revealed that it is likely to have undergone a barium-enrichment phase in its evolution because of a higher mass companion. Despite this, our study reveals that the star has a fairly typical activity level for its rotation period and spectral type. Future studies will enable us to explore the long-term evolution of the field, as well as to measure the stellar rotation period, with greater accuracy.

astro-ph.SR↗

arXiv2014

The role of magnetic fields in pre-main sequence stars

Strong, kilo-Gauss, magnetic fields are required to explain a range of observational properties in young, accreting pre-main sequence (PMS) systems. We review the techniques used to detect magnetic fields in PMS stars. Key results from a long running campaign aimed at characterising the large scale magnetic fields in accreting T Tauri stars are presented. Maps of surface magnetic flux in these systems can be used to build 3-D models exploring the role of magnetic fields and the efficiency with which magnetic fields can channel accretion from circumstellar disks on to young stars. Long-term variability in T Tauri star magnetic fields strongly point to a dynamo origin of the magnetic fields. Studies are underway to quantify how changes in magnetic fields affect their accretion properties. We also present the first results from a new programme that investigates the evolution of magnetic fields in intermediate mass (1.5-3 Msun) pre-main sequence stars as they evolve from being convective T Tauri stars to fully radiative Herbig AeBe stars.

astro-ph.SR↗

arXiv2012

The magnetic fields and magnetospheres of hot stars

Strong advances in direct evidence of magnetic fields in hot massive stars have been possible thanks to the new generation of high-resolution spectropolarimeters such as ESPaDOnS (on the Canada-France-Hawaii Telescope) or HARPSpol (on the 3.6m ESO telescope). UV and optical high-resolution spectroscopy has also been very useful to study the magnetospheres of massive stars. In this contribution I review the observing tools and our current knowledge concerning the detection and characterisation of the magnetic fields and magnetospheres in hot stars.

astro-ph.SR↗

arXiv2011

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.

astro-ph.SR↗