Context. Although debris discs have been detected around a significant number of main-sequence stars, only a few of them are known to harbour hot dust in their inner part where terrestrial planets ...may have formed. Thanks to infrared interferometric observations, it is possible to obtain a direct measurement of these regions, which are of prime importance for preparing future exo-Earth characterisation missions. Aims. We resolve the exozodiacal dust disc around Vega with the help of infrared stellar interferometry and estimate the integrated H-band flux originating from the first few AUs of the debris disc. Methods. Precise H-band interferometric measurements were obtained on Vega with the 3-telescope IOTA/IONIC interferometer (Mount Hopkins, Arizona). Thorough modelling of both interferometric data (squared visibility and closure phase) and spectral energy distribution was performed to constrain the nature of the near-infrared excess emission. Results. Resolved circumstellar emission within ~6 AU from Vega is identified at the 3-σ level. The most straightforward scenario consists in a compact dust disc producing a thermal emission that is largely dominated by small grains located between 0.1 and 0.3 AU from Vega and accounting for 1.23 ± 0.45% of the near-infrared stellar flux for our best-fit model. This flux ratio is shown to vary slightly with the geometry of the model used to fit our interferometric data (variations within ± 0.19%). Conclusions. The presence of hot exozodiacal dust in the vicinity of Vega, initially revealed by K-band CHARA/FLUOR observations, is confirmed by our H-band IOTA/IONIC measurements. Whereas the origin of the dust is still uncertain, its presence and the possible connection with the outer disc suggest that the Vega system is currently undergoing major dynamical perturbations.
Aims.
We aim to demonstrate that the presence and mass of an exoplanet can now be effectively derived from the astrometry of another exoplanet.
Methods.
We combined previous astrometry of
β
Pictoris ...b with a new set of observations from the GRAVITY interferometer. The orbital motion of
β
Pictoris b is fit using Markov chain Monte Carlo simulations in Jacobi coordinates. The inner planet,
β
Pictoris c, was also reobserved at a separation of 96 mas, confirming the previous orbital estimations.
Results.
From the astrometry of planet b only, we can (i) detect the presence of
β
Pictoris c and (ii) constrain its mass to 10.04
−3.10
+4.53
M
Jup
. If one adds the astrometry of
β
Pictoris c, the mass is narrowed down to 9.15
−1.06
+1.08
M
Jup
. The inclusion of radial velocity measurements does not affect the orbital parameters significantly, but it does slightly decrease the mass estimate to 8.89
−0.75
+0.75
M
Jup
. With a semimajor axis of 2.68 ± 0.02 au, a period of 1221 ± 15 days, and an eccentricity of 0.32 ± 0.02, the orbital parameters of
β
Pictoris c are now constrained as precisely as those of
β
Pictoris b. The orbital configuration is compatible with a high-order mean-motion resonance (7:1). The impact of the resonance on the planets’ dynamics would then be negligible with respect to the secular perturbations, which might have played an important role in the eccentricity excitation of the outer planet.
The GRAVITY Young Stellar Object survey Perraut, K.; Labadie, L.; Lazareff, B. ...
Astronomy and astrophysics (Berlin),
12/2019, Volume:
632
Journal Article
Peer reviewed
Open access
Context.
The formation and the evolution of protoplanetary disks are important stages in the lifetime of stars. Terrestrial planets form or migrate within the innermost regions of these ...protoplanetary disks and so, the processes of disk evolution and planet formation are intrinsically linked. Studies of the dust distribution, composition, and evolution of these regions are crucial to understanding planet formation.
Aims.
We built a homogeneous observational dataset of Herbig Ae/Be disks with the aim of spatially resolving the sub au-scale region to gain a statistical understanding of their morphological and compositional properties, in addition to looking for correlations with stellar parameters, such as luminosity, mass, and age.
Methods.
We observed 27 Herbig Ae/Be stars with the GRAVITY instrument installed at the combined focus of the Very Large Telescope Interferometer (VLTI) and operating in the near-infrared
K
-band, focused on the
K
-band thermal continuum, which corresponds to stellar flux reprocessed by the dust grains. Our sample covers a large range of effective temperatures, luminosities, masses, and ages for the intermediate-mass star population. The circumstellar disks in our sample also cover a range of various properties in terms of reprocessed flux, flared or flat morphology, and gaps. We developed semi-physical geometrical models to fit our interferometric data.
Results.
Our best-fit models correspond to smooth and wide rings that support previous findings in the
H
-band, implying that wedge-shaped rims at the dust sublimation edge are favored. The measured closure phases are generally non-null with a median value of ~10°, indicating spatial asymmetries of the intensity distributions. Multi-size grain populations could explain the closure phase ranges below 20–25° but other scenarios should be invoked to explain the largest ones. Our measurements extend the Radius-Luminosity relation to ~10
4
L
⊙
luminosity values and confirm the significant spread around the mean relation observed by PIONIER in the
H
-band. Gapped sources exhibit a large
N
-to-
K
band size ratio and large values of this ratio are only observed for the members of our sample that would be older than 1 Ma, less massive, and with lower luminosity. In the mass range of 2
M
⊙
, we do observe a correlation in the increase of the relative age with the transition from group II to group I, and an increase of the
N
-to-
K
size ratio. However, the size of the current sample does not yet permit us to invoke a clear, universal evolution mechanism across the Herbig Ae/Be mass range. The measured locations of the
K
-band emission in our sample suggest that these disks might be structured by forming young planets, rather than by depletion due to EUV, FUV, and X-ray photo-evaporation.
Context. To understand the chemical composition of planets, it is important to know the chemical composition of the region where they form in protoplanetary disks. Because of its fundamental role in ...chemical and biological processes, carbon is a key element to trace. Aims. We identify the carriers and processes behind the extended near-infrared (NIR) flux observed around several Herbig stars. Methods. We compared the extended NIR flux from objects in the PIONIER Herbig Ae/Be survey with their flux in the policyclic aromatic hydrocarbon (PAH) features. HD 100453 is used as a benchmark case to investigate the influence of quantum heated particles, like PAHs or very small carbonaceous grains, in more detail. We use the Monte Carlo radiative transfer code MCMax to do a parameter study of the quantum heated particle (QHP) size and scale height and examine the influence of quantum heating on the amount of extended flux in the NIR visibilities. Results. There is a correlation between the PAH feature flux of a disk and the amount of its extended NIR flux. We find that very small carbonaceous grains create the observed extended NIR flux around HD 100453 and still lead to a realistic SED. These results cannot be achieved without using quantum heating effects, e.g. only with scattered light and grains in thermal equilibrium. Conclusions. It is possible to explain the extended NIR emission around Herbig stars with the presence of carbonaceous, quantum heated particles. Interferometric observations can be used to constrain the spatial distribution and typical size of carbonaceous material in the terrestrial planet forming region.
Context. PIONIER stands for Precision Integrated-Optics Near-infrared Imaging ExpeRiment. It combines four 1.8m Auxilliary Telescopes or four 8m Unit Telescopes of the Very Large Telescope ...Interferometer (ESO, Chile) using an integrated optics combiner. The instrument was integrated at IPAG in December 2009 and commissioned at the Paranal Observatory in October 2010. It has provided scientific observations since November 2010. Aims. In this paper, we explain the instrumental concept and describe the standard operational modes and the data reduction strategy. We present the typical performance and discuss how to improve them. Methods. This paper is based on laboratory data obtained during the integrations at IPAG, as well as on-sky data gathered during the commissioning at VLTI. We illustrate the imaging capability of PIONIER on the binaries δ Sco and HIP11231. Results. PIONIER provides six visibilities and three independent closure phases in the H band, either in a broadband mode or with a low spectral dispersion (R = 40), using natural light (i.e. unpolarized). The limiting magnitude is Hmag = 7 in dispersed mode under median atmospheric conditions (seeing < 1, τ0 > 3ms) with the 1.8m Auxiliary Telescopes. We demonstrate a precision of 0.5deg on the closure phases. The precision on the calibrated visibilities ranges from 3% to 15% depending on the atmospheric conditions. Conclusions. PIONIER was installed and successfully tested as a visitor instrument for the VLTI. It permits high angular resolution imaging studies at an unprecedented level of sensitivity. The successful combination of the four 8m Unit Telescopes in March 2011 demonstrates that VLTI is ready for four-telescope operation.
Context.
In the Milky Way the central massive black hole, Sgr A
*
, coexists with a compact nuclear star cluster that contains a sub-parsec concentration of fast-moving young stars called S-stars. ...Their location and age are not easily explained by current star formation models, and in several scenarios the presence of an intermediate-mass black hole (IMBH) has been invoked.
Aims.
We use GRAVITY astrometric and SINFONI, KECK, and GNIRS spectroscopic data of S2, the best known S-star, to investigate whether a second massive object could be present deep in the Galactic Centre (GC) in the form of an IMBH binary companion to Sgr A
*
.
Methods.
To solve the three-body problem, we used a post-Newtonian framework and consider two types of settings: (i) a hierarchical set-up where the star S2 orbits the Sgr A
*
–IMBH binary and (ii) a non-hierarchical set-up where the IMBH trajectory lies outside the S2 orbit. In both cases we explore the full 20-dimensional parameter space by employing a Bayesian dynamic nested sampling method.
Results.
For the hierarchical case we find the strongest constraints: IMBH masses > 2000
M
⊙
on orbits with smaller semi-major axes than S2 are largely excluded. For the non-hierarchical case, the chaotic nature of the problem becomes significant: the parameter space contains several pockets of valid IMBH solutions. However, a closer analysis of their impact on the resident stars reveals that IMBHs on semi-major axes larger than S2 tend to disrupt the S-star cluster in less than a million years. This makes the existence of an IMBH among the S-stars highly unlikely.
Conclusions.
The current S2 data do not formally require the presence of an IMBH. If an IMBH hides in the GC, it has to be either a low-mass IMBH inside the S2 orbit that moves on a short and significantly inclined trajectory or an IMBH with a semi-major axis > 1″. We provide the parameter maps of valid IMBH solutions in the GC and discuss the general structure of our results and how future observations can help to put even stronger constraints on the properties of IMBHs in the GC.
The GRAVITY young stellar object survey Wojtczak, J. A.; Labadie, L.; Perraut, K. ...
Astronomy and astrophysics (Berlin),
01/2023, Volume:
669, Issue:
A59
Journal Article
Peer reviewed
Open access
Context.
Hot atomic hydrogen emission lines in pre-main sequence stars serve as tracers for physical processes in the innermost regions of circumstellar accretion disks, where the interaction between ...a star and disk is the dominant influence on the formation of infalls and outflows. In the highly magnetically active T Tauri stars, this interaction region is particularly shaped by the stellar magnetic field and the associated magnetosphere, covering the inner five stellar radii around the central star. Even for the closest T Tauri stars, a region as compact as this is only observed on the sky plane at sub-mas scales. To resolve it spatially, the capabilities of optical long baseline interferometry are required.
Aims.
We aim to spatially and spectrally resolve the Brγ hydrogen emission line with the methods of interferometry in order to examine the kinematics of the hydrogen gas emission region in the inner accretion disk of a sample of solar-like young stellar objects. The goal is to identify trends and categories among the sources of our sample and to discuss whether or not they can be tied to different origin mechanisms associated with Brγ emission in T Tauri stars, chiefly and most prominently magnetospheric accretion.
Methods.
We observed a sample of seven T Tauri stars for the first time with VLTI GRAVITY, recording spectra and spectrally dispersed interferometric quantities across the Brγ line at 2.16 µm in the near-infrared
K
-band. We used the visibilities and differential phases to extract the size of the Brγ emission region and the photocentre shifts on a channel-by-channel basis, probing the variation of spatial extent at different radial velocities. To assist in the interpretation, we also made use of radiative transfer models of magnetospheric accretion to establish a baseline of expected interferometric signatures if accretion is the primary driver of Brγ emission.
Results.
From among our sample, we find that five of the seven T Tauri stars show an emission region with a half-flux radius in the four to seven stellar radii range that is broadly expected for magnetospheric truncation. Two of the five objects also show Brγ emission primarily originating from within the co-rotation radius, which is an important criterion for magnetospheric accretion. Two objects exhibit extended emission on a scale beyond 10
R
*
, one of them is even beyond the
K
-band continuum half-flux radius of 11.3
R
*
. The observed photocentre shifts across the line can be either similar to what is expected for disks in rotation or show patterns of higher complexity.
Conclusions.
Based on the observational findings and the comparison with the radiative transfer models, we find strong evidence to suggest that for the two weakest accretors in the sample, magnetospheric accretion is the primary driver of Brγ radiation. The results for the remaining sources imply either partial or strong contributions coming from additional, spatially extended emission components in the form of outflows, such as stellar or disk winds. We expect that in actively accreting T Tauri stars, these phenomena typically occur simultaneously on different spatial scales. Through more advanced modelling, interferometry will be a key factor in disentangling their distinct contributions to the total Brγ flux arising from the innermost disk regions.
ABSTRACT
Double-lined spectroscopic binaries (SB2s) are one of the main sources of stellar masses, as additional observations are only needed to give the inclinations of the orbital planes in order ...to obtain the individual masses of the components. For this reason, we are observing a selection of SB2s using the SOPHIE spectrograph at the Haute-Provence observatory in order to precisely determine their orbital elements. Our objective is to finally obtain masses with an accuracy of the order of one per cent by combining our radial velocity (RV) measurements and the astrometric measurements that will come from the Gaia satellite. We present here the RVs and the re-determined orbits of 10 SB2s. In order to verify the masses, we will derive from Gaia, we obtained interferometric measurements of the ESO VLTI for one of these SB2s. Adding the interferometric or speckle measurements already published by us or by others for four other stars, we finally obtain the masses of the components of five binary stars, with masses ranging from 0.51 to 2.2 solar masses, including main-sequence dwarfs and some more evolved stars whose location in the HR diagram has been estimated.
Aims. We discuss the spin-orbit orientation of the Fomalhaut planetary system composed of a central A4V star, a debris disk, and a recently discovered planetary companion. Methods. We use spectrally ...resolved, near-IR long baseline interferometry to obtain precise spectro-astrometric measurements across the Br-${\gamma}$ absorption line. The achieved astrometric accuracy of ${\pm}3~\mu$as and the spectral resolution $R=1500$ from the AMBER/VLTI instrument allow us to spatially and spectrally resolve the rotating photosphere. Results. We find a position angle ${{\rm PA_{star}}}=65\degr$ ± $3\degr$ for the stellar rotation axis, perpendicular to the literature measurement for the disk position angle (${{\rm PA_{disk}}}=156\fdg0$ ± $0\fdg3$). This is the first time such a test could be performed for a debris disk, and in a non-eclipsing system. Additionally, our measurements suggest unexpected backward-scattering properties for the circumstellar dust grains. Conclusions. Our observations validate the standard scenario for star and planet formation in which the angular momentum of the planetary systems are expected to be colinear with the stellar spins.
Context. The triple system HD 150136 is composed of an O3 V((f*))–O3.5 V((f+)) primary, of an O5.5–6 V((f)) secondary, and of a more distant O6.5–7 V((f)) tertiary. The latter component went through ...periastron in 2015–2016, an event that will not occur again within the next eight years. Aims. We aim to analyse the tertiary periastron passage to determine the orbital properties of the outer system, to constrain its inclination and its eccentricity, and to determine the actual masses of the three components of the system. Methods. We conducted an intensive spectroscopic monitoring of the periastron passage of the tertiary component and combined the outcoming data with new interferometric measurements. This allows us to derive the orbital solution of the outer orbit in three-dimensional space. We also obtained the light curve of the system to further constrain the inclination of the inner binary. Results. We determine an orbital period of 8.61 ± 0.02 years, an eccentricity of 0.682 ± 0.002, and an inclination of 106.18 ± 0.14° for the outer orbit. The actual masses of the inner system and of the tertiary object are 72.32−8.49+8.45 $72.32_{-8.49}^{+8.45}$72.32−8.49+8.45 M⊙ and 15.54−4.97+4.96 $15.54_{-4.97}^{+4.96}$15.54−4.97+4.96 M⊙, respectively. From the mass of the inner system and accounting for the known mass ratio between the primary and the secondary, we determine actual masses of 42.81 M⊙ and 29.51 M⊙ for the primary and the secondary components, respectively. We infer, from the different mass ratios and the inclination of the outer orbit, an inclination of 62.4° for the inner system. This value is confirmed by photometry. Grazing eclipses and ellipsoidal variations are detected in the light curve of HD 150136. We also compute the distance of the system to 1.096 ± 0.274 kpc. Conclusions. By combining spectroscopy, interferometry, and photometry, HD 150136 offers us a unique chance to compare theory and observations. The masses estimated through our analysis are smaller than those constrained by evolutionary models. The formation of this triple system suggests similar ages for the three components within the errorbars. Finally, we show that Lidov–Kozai cycles have no effect on the evolution of the inner binary, which suggests that the latter will experience mass transfer leading to a merger of the two stars.
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