Context.
T Tauri stars are surrounded by dust and gas disks. As material reservoirs from which matter is accreted onto the central star and planets are built, these protoplanetary disks play a ...central role in star and planet formation.
Aims.
We aim at spatially resolving at sub-astronomical unit (sub-au) scales the innermost regions of the protoplanetary disks around a sample of T Tauri stars to better understand their morphology and composition.
Methods.
Thanks to the sensitivity and the better spatial frequency coverage of the GRAVITY instrument of the Very Large Telescope Interferometer, we extended our homogeneous data set of 27 Herbig stars and collected near-infrared
K
-band interferometric observations of 17 T Tauri stars, spanning effective temperatures and luminosities in the ranges of ~4000–6000 K and ~0.4–10
L
⊙
, respectively. We focus on the continuum emission and develop semi-physical geometrical models to fit the interferometric data and search for trends between the properties of the disk and the central star.
Results.
As for those of their more massive counterparts, the Herbig Ae/Be stars, the best-fit models of the inner rim of the T Tauri disks correspond to wide rings. The GRAVITY measurements extend the radius-luminosity relation toward the smallest luminosities (0.4–10
L
⊙
). As observed previously, in this range of luminosities, the
R
∝
L
1∕2
trend line is no longer valid, and the
K
-band sizes measured with GRAVITY appear to be larger than the predicted sizes derived from sublimation radius computation. We do not see a clear correlation between the
K
-band half-flux radius and the mass accretion rate onto the central star. Besides, having magnetic truncation radii in agreement with the
K
-band GRAVITY sizes would require magnetic fields as strong as a few kG, which should have been detected, suggesting that accretion is not the main process governing the location of the half-flux radius of the inner dusty disk. The GRAVITY measurements agree with models that take into account the scattered light, which could be as important as thermal emission in the
K
band for these cool stars. The
N
-to-
K
band size ratio may be a proxy for disentangling disks with silicate features in emission from disks with weak and/or in absorption silicate features (i.e., disks with depleted inner regions and/or with large gaps). The GRAVITY data also provide inclinations and position angles of the inner disks. When compared to those of the outer disks derived from ALMA images of nine objects of our sample, we detect clear misalignments between both disks for four objects.
Conclusions.
The combination of improved data quality with a significant and homogeneous sample of young stellar objects allows us to revisit the pioneering works done on the protoplanetary disks by
K
-band interferometry and to test inner disk physics such as the inner rim morphology and location.
The GRAVITY young stellar object survey Garcia Lopez, R.; Natta, A.; Fedriani, R. ...
Astronomy and astrophysics (Berlin),
04/2024, Letnik:
684
Journal Article
Recenzirano
Odprti dostop
Context . The region of protoplanetary disks closest to a star (within 1–2 au) is shaped by a number of different processes, from accretion of the disk material onto the central star to ejection in ...the form of winds and jets. Optical and near-IR emission lines are potentially good tracers of inner disk processes if very high spatial and/or spectral resolution are achieved. Aims . In this paper, we exploit the capabilities of the VLTI-GRAVITY near-IR interferometer to determine the location and kinematics of the hydrogen emission line Br γ . Methods . We present VLTI-GRAVITY observations of the Br γ line for a sample of 26 stars of intermediate mass (HAEBE), the largest sample so far analysed with near-IR interferometry. Results . The Br γ line was detected in 17 objects. The emission is very compact (in most cases only marginally resolved), with a size of 10–30 R * (1–5 mas). About half of the total flux comes from even smaller regions, which are unresolved in our data. For eight objects, it was possible to determine the position angle (PA) of the line-emitting region, which is generally in agreement with that of the inner-dusty disk emitting the K -band continuum. The position-velocity pattern of the Br γ line-emitting region of the sampled objects is roughly consistent with Keplerian rotation. The exception is HD 45677, which shows more extended emission and more complex kinematics. The most likely scenario for the Br γ origin is that the emission comes from an MHD wind launched very close to the central star, in a region well within the dust sublimation radius. An origin in the bound gas layer at the disk surface cannot be ruled out, while accreting matter provides only a minor fraction of the total flux. Conclusions . These results show the potential of near-IR spectro-interferometry to study line emission in young stellar objects.
The GRAVITY young stellar object survey Bouarour, Y.-I.; Perraut, K.; Ménard, F. ...
Astronomy and astrophysics (Berlin),
10/2020, Letnik:
642
Journal Article
Recenzirano
Odprti dostop
Context.
Studies of the dust distribution, composition, and evolution of protoplanetary disks provide clues for understanding planet formation. However, little is known about the innermost regions of ...disks where telluric planets are expected to form.
Aims.
We aim constrain the geometry of the inner disk of the T Tauri star RY Lup by combining spectro-photometric data and interferometric observations in the near-infrared (NIR) collected at the Very Large Telescope Interferometer. We use PIONIER data from the ESO archive and GRAVITY data that were obtained in June 2017 with the four 8m telescopes.
Methods.
We use a parametric disk model and the 3D radiative transfer code MCFOST to reproduce the spectral energy distribution (SED) and match the interferometric observations. MCFOST produces synthetic SEDs and intensity maps at different wavelengths from which we compute the modeled interferometric visibilities and closure phases through Fourier transform.
Results.
To match the SED from the blue to the millimetric range, our model requires a stellar luminosity of 2.5
L
⊙
, higher than any previously determined values. Such a high value is needed to accommodate the circumstellar extinction caused by the highly inclined disk, which has been neglected in previous studies. While using an effective temperature of 4800 K determined through high-resolution spectroscopy, we derive a stellar radius of 2.29
R
⊙
. These revised fundamental parameters, when combined with the mass estimates available (in the range 1.3–1.5
M
⊙
), lead to an age of 0.5–2.0 Ma for RY Lup, in better agreement with the age of the Lupus association than previous determinations. Our disk model (that has a transition disk geometry) nicely reproduces the interferometric GRAVITY data and is in good agreement with the PIONIER ones. We derive an inner rim location at 0.12 au from the central star. This model corresponds to an inclination of the inner disk of 50°, which is in mild tension with previous determinations of a more inclined outer disk from SPHERE (70° in NIR) and ALMA (67 ± 5°) images, but consistent with the inclination determination from the ALMA CO spectra (55 ± 5°). Increasing the inclination of the inner disk to 70° leads to a higher line-of-sight extinction and therefore requires a higher stellar luminosity of 4.65
L
⊙
to match the observed flux levels. This luminosity would translate to a stellar radius of 3.13
R
⊙
, leading to an age of 2–3 Ma, and a stellarmass of about 2
M
⊙
, in disagreement with the observed dynamical mass estimate of 1.3–1.5
M
⊙
. Critically, this high-inclination inner disk model also fails to reproduce the visibilities observed with GRAVITY.
Conclusions.
The inner dust disk, as traced by the GRAVITY data, is located at a radius in agreement with the dust sublimation radius. An ambiguity remains regarding the respective orientations of the inner and outer disk, coplanar and mildly misaligned, respectively.As our datasets are not contemporary and the star is strongly variable, a deeper investigation will require a dedicated multi-technique observing campaign.
The GRAVITY young stellar object survey Bouarour, Y.-I.; Garcia Lopez, R.; Sanchez-Bermudez, J. ...
Astronomy and astrophysics (Berlin),
02/2024, Letnik:
682
Journal Article
Recenzirano
Odprti dostop
Aims . We aim to investigate the origin of the HI Br γ emission in young stars by using GRAVITY to image the innermost region of circumstellar disks, where important physical processes such as ...accretion and winds occur. With high spectral and angular resolution, we focus on studying the continuum and the HI Br γ -emitting area of the Herbig star HD 58647. Methods . Using VLTI-GRAVITY, we conducted observations of HD 58647 with both high spectral and high angular resolution. Thanks to the extensive uv coverage, we were able to obtain detailed images of the circumstellar environment at a sub-au scale, specifically capturing the continuum and the Br γ -emitting region. Through the analysis of velocity-dispersed images and photocentre shifts, we were able to investigate the kinematics of the HI Br γ -emitting region. Results . The recovered continuum images show extended emission where the disk major axis is oriented along a position angle of 14°. The size of the continuum emission at 5 -σ levels is ~1.5 times more extended than the sizes reported from geometrical fitting (3.69 mas ± 0.02 mas). This result supports the existence of dust particles close to the stellar surface, screened from the stellar radiation by an optically thick gaseous disk. Moreover, for the first time with GRAVITY, the hot gas component of HD 58647 traced by the Brγ has been imaged. This allowed us to constrain the size of the Br γ -emitting region and study the kinematics of the hot gas; we find its velocity field to be roughly consistent with gas that obeys Keplerian motion. The velocity-dispersed images show that the size of the hot gas emission is from a more compact region than the continuum (2.3 mas ± 0.2 mas). Finally, the line phases show that the emission is not entirely consistent with Keplerian rotation, hinting at a more complex structure in the hot gaseous disk.
The GRAVITY young stellar object survey R. Garcia Lopez; A. Natta; Fedriani, R ...
Astronomy and astrophysics (Berlin),
04/2024, Letnik:
684
Journal Article
Recenzirano
Context. The region of protoplanetary disks closest to a star (within 1–2 au) is shaped by a number of different processes, from accretion of the disk material onto the central star to ejection in ...the form of winds and jets. Optical and near-IR emission lines are potentially good tracers of inner disk processes if very high spatial and/or spectral resolution are achieved. Aims. In this paper, we exploit the capabilities of the VLTI-GRAVITY near-IR interferometer to determine the location and kinematics of the hydrogen emission line Brγ. Methods. We present VLTI-GRAVITY observations of the Brγ line for a sample of 26 stars of intermediate mass (HAEBE), the largest sample so far analysed with near-IR interferometry. Results. The Brγ line was detected in 17 objects. The emission is very compact (in most cases only marginally resolved), with a size of 10–30 R*(1–5 mas). About half of the total flux comes from even smaller regions, which are unresolved in our data. For eight objects, it was possible to determine the position angle (PA) of the line-emitting region, which is generally in agreement with that of the inner-dusty disk emitting the K-band continuum. The position-velocity pattern of the Brγ line-emitting region of the sampled objects is roughly consistent with Keplerian rotation. The exception is HD 45677, which shows more extended emission and more complex kinematics. The most likely scenario for the Brγ origin is that the emission comes from an MHD wind launched very close to the central star, in a region well within the dust sublimation radius. An origin in the bound gas layer at the disk surface cannot be ruled out, while accreting matter provides only a minor fraction of the total flux. Conclusions. These results show the potential of near-IR spectro-interferometry to study line emission in young stellar objects.
We aim to investigate the origin of the HI Br\(\gamma\) emission in young stars by using GRAVITY to image the innermost region of circumstellar disks, where important physical processes such as ...accretion and winds occur. With high spectral and angular resolution, we focus on studying the continuum and the HI Br\(\gamma\)-emitting area of the Herbig star HD58647. Using VLTI-GRAVITY, we conducted observations of HD58647 with both high spectral and high angular resolution. Thanks to the extensive \(uv\) coverage, we were able to obtain detailed images of the circumstellar environment at a sub-au scale, specifically capturing the continuum and the Br\(\gamma\)-emitting region. Through the analysis of velocity-dispersed images and photocentre shifts, we were able to investigate the kinematics of the HI Br\(\gamma\)-emitting region. The recovered continuum images show extended emission where the disk major axis is oriented along a position angle of 14\degr. The size of the continuum emission at 5-sigma levels is \(\sim\) 1.5 times more extended than the sizes reported from geometrical fitting (3.69 mas \(\pm\) 0.02 mas). This result supports the existence of dust particles close to the stellar surface, screened from the stellar radiation by an optically thick gaseous disk. Moreover, for the first time with GRAVITY, the hot gas component of HD58647 traced by the Br\(\gamma\) ,has been imaged. This allowed us to constrain the size of the Br\(\gamma\)-emitting region and study the kinematics of the hot gas; we find its velocity field to be roughly consistent with gas that obeys Keplerian motion. The velocity-dispersed images show that the size of the hot gas emission is from a more compact region than the continuum (2.3 mas \(\pm\) 0.2 mas). Finally, the line phases show that the emission is not entirely consistent with Keplerian rotation, hinting at a more complex structure in the hot gaseous disk.
These protoplanetary disks in T Tauri stars play a central role in star and planet formation. We spatially resolve at sub-au scales the innermost regions of a sample of T Tauri's disks to better ...understand their morphology and composition. We extended our homogeneous data set of 27 Herbig stars and collected near-IR K-band observations of 17 T Tauri stars, spanning effective temperatures and luminosities in the ranges of ~4000-6000 K and ~0.4-10 Lsun. We focus on the continuum emission and develop semi-physical geometrical models to fit the interferometric data and search for trends between the properties of the disk and the central star. The best-fit models of the disk's inner rim correspond to wide rings. We extend the Radius-luminosity relation toward the smallest luminosities (0.4-10 Lsun) and find the R~L^(1/2) trend is no longer valid, since the K-band sizes measured with GRAVITY are larger than the predicted sizes from sublimation radius computation. No clear correlation between the K-band half-flux radius and the mass accretion rate is seen. Having magnetic truncation radii in agreement with the K-band GRAVITY sizes would require magnetic fields as strong as a few kG, which should have been detected, suggesting that accretion is not the main process governing the location of the half-flux radius of the inner dusty disk. Our measurements agree with models that take into account the scattered light. The N-to-K band size ratio may be a proxy for disentangling disks with silicate features in emission from disks with weak and/or in absorption silicate features. When comparing inclinations and PA of the inner disks to those of the outer disks (ALMA) in nine objects of our sample, we detect misalignments for four objects.
We use PIONIER data from the ESO archive and GRAVITY data that were obtained in June 2017 with the four 8m telescopes. We use a parametric disk model and the 3D radiative transfer code MCFOST to ...reproduce the Spectral Energy Distribution and match the interferometric observations. To match the SED , our model requires a stellar luminosity of 2.5 Lsun, higher than any previously determined values. Such a high value is needed to accommodate the circumstellar extinction caused by the highly inclined disk, which has been neglected in previous studies. While using an effective temperature of 4800 K determined through high-resolution spectroscopy, we derive a stellar radius of 2.29 Rsun. These revised fundamental parameters, when combined with the mass estimates available , lead to an age of 0.5-2.0 Ma for RY Lup, in better agreement with the age of the Lupus association than previous determinations. Our disk model nicely reproduces the interferometric GRAVITY data and is in good agreement with the PIONIER ones. We derive an inner rim location at 0.12~au from the central star. This model corresponds to an inclination of the inner disk of 50deg, which is in mild tension with previous determinations of a more inclined outer disk from SPHERE (70 deg in NIR) and ALMA(67 \(\pm\)5 deg) images, but consistent with the inclination determination from the ALMA CO spectra (55\(\pm\)5deg). Increasing the inclination of the inner disk to 70 deg leads to a higher line-of-sight extinction and therefore requires a higher stellar luminosity of 4.65 Lsun to match the observed flux levels. This luminosity would translate to a stellar radius of 3.13~Rsun, leading to an age of 2-3~Ma, and a stellar mass of about 2 Msun, in disagreement with the observed dynamical mass estimate of 1.3-1.5 Msun. Critically, this high-inclination inner disk model also fails to reproduce the visibilities observed with GRAVITY.
The region of protoplanetary disks closest to a star (within 1-2\,au) is
shaped by a number of different processes, from accretion of the disk material
onto the central star to ejection in the form ...of winds and jets. Optical and
near-IR emission lines are potentially good tracers of inner disk processes if
very high spatial and/or spectral resolution are achieved. In this paper, we
exploit the capabilities of the VLTI-GRAVITY near-IR interferometer to
determine the location and kinematics of the hydrogen emission line Bracket
gamma. We present VLTI-GRAVITY observations of the Bracket gamma line for a
sample of 26 stars of intermediate mass (HAEBE), the largest sample so far
analysed with near-IR interferometry. The Bracket gamma line was detected in 17
objects. The emission is very compact (in most cases only marginally resolved),
with a size of 10-30R* (1-5 mas). About half of the total flux comes from even
smaller regions, which are unresolved in our data. For eight objects, it was
possible to determine the position angle (PA) of the line-emitting region,
which is generally in agreement with that of the inner-dusty disk emitting the
K-band continuum. The position-velocity pattern of the Bracket gamma
line-emitting region of the sampled objects is roughly consistent with
Keplerian rotation. The exception is HD~45677, which shows more extended
emission and more complex kinematics. The most likely scenario for the Bracket
gamma origin is that the emission comes from an MHD wind launched very close to
the central star, in a region well within the dust sublimation radius. An
origin in the bound gas layer at the disk surface cannot be ruled out, while
accreting matter provides only a minor fraction of the total flux. These
results show the potential of near-IR spectro-interferometry to study line
emission in young stellar objects.
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