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ExPo image of the circumstellar environment of SU Aur in polarised intensity (P I ), taken without a filter. The intensity scale is logarithmic over two orders of magnitude and the length of the vectors represents a lower limit to the true polarisation degree. North is up and east is to the left.
Source publication
The circumstellar environments of classical T Tauri stars are challenging to
directly image because of their high star-to-disk contrast ratio. One method to
overcome this is by using imaging polarimetry where scattered and consequently
polarised starlight from the star's circumstellar disk can be separated from
the unpolarised light of the central...
Contexts in source publication
Context 1
... resulting ExPo image of SU Aur in linearly polarised light is shown in Figure 1. The image is zoomed-in to highlight the structure observed in the inner parts of the ExPo image. ...
Context 2
... Figure 2 we show the resulting model at fixed inclination angles. From these models we conclude that the model with an inclination angle of 50 • reproduces the observed polarimetric image best (ref Figure 1). The dark lane through the centre of the polarised intensity image is a result of the subtraction of the polarisation of the central component, which was made to correct any residual instrumental polarisation. ...
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Citations
... The main feature of SU Aur is a large tail (Chakraborty & Ge 2004;Jeffers et al. 2014;de Leon et al. 2015) extending outwards to up to 1000 au on the west side of the disk. While multiple explanations for this arm have been proposed, such as a cloud remnant (Jeffers et al. 2014) or a collision with a stellar intruder (Akiyama et al. 2019), recent work by Ginski et al. (2021) shows that, by using results reported here, the tails (both the large tail in the west and the shorter one in the north) originate from still infalling material. ...
... The main feature of SU Aur is a large tail (Chakraborty & Ge 2004;Jeffers et al. 2014;de Leon et al. 2015) extending outwards to up to 1000 au on the west side of the disk. While multiple explanations for this arm have been proposed, such as a cloud remnant (Jeffers et al. 2014) or a collision with a stellar intruder (Akiyama et al. 2019), recent work by Ginski et al. (2021) shows that, by using results reported here, the tails (both the large tail in the west and the shorter one in the north) originate from still infalling material. In Figure 12, we show the polarimetric and full intensity scattered light SPHERE data taken on 14 December 2019. ...
Context. Distinguishing the signal from young gas-rich circumstellar disks from the stellar signal in near-infrared (NIR) light is a difficult task. Multiple techniques have been developed over the years of which angular differential imaging (ADI) and polarimetric differential imaging (PDI) have been most successful. However, both techniques cope with drawbacks such as self-subtraction. To address these drawbacks, we explore iterative ADI (IADI) techniques to increase signal throughput in total intensity observations.
Aims. The aim of this work is to explore the effectiveness of IADI in recovering the self-subtracted regions of disks by applying ADI techniques iteratively.
Methods. IADI works by feeding back all positive signal of the result from standard ADI over multiple iterations. To determine the effectiveness of IADI, a model of a disk image is made and post-processed with IADI. We explored two versions of IADI, classical IADI, which uses the median of the data set to reconstruct the point spread function (PSF), and PCA-IADI, which uses principal component analysis to model the PSF. In addition, we explored masking based on polarimetric images and a signal threshold for feeding back signal.
Results. Asymmetries are a very important factor in recovering the disk because these lead to less overlap of the disk in the data set. In some cases, we were able to recover a factor ~75 more flux with IADI than with ADI. The Procrustes distance is used to quantify the impact of the algorithm on the scattering phase function. Depending on the level of noise and the ratio between the stellar signal and disk signal, the phase function can be recovered a factor 6.4 in Procrustes distance better than standard ADI. Amplification and smearing of noise over the image due to many iterations did occur. By using binary masks and a dynamic threshold this feedback was mitigated, but it is still a problem in the final pipeline. Finally, observations of protoplanetary disks made with VLT/SPHERE were processed with IADI giving rise to very promising results.
Conclusions. While IADI has problems with low-signal-to-noise-ratio (S/N) observations due to noise amplification and star reconstruction, higher S/N observations show promising results with respect to standard ADI.
... The main feature of SU Aur is a large tail (Chakraborty & Ge 2004;Jeffers et al. 2014;de Leon et al. 2015) extending outwards to up to 1000 au on the west side of the disk. While multiple explanations of this arm have been proposed such as a cloud remnant (Jeffers et al. 2014) or a collision with a stellar intruder (Akiyama et al. 2019), recent work by (Ginski et al. 2021) shows that, by using results reported here, the tails (both the large tail in the west and the shorter one in the north) originate from still infalling material. ...
... The main feature of SU Aur is a large tail (Chakraborty & Ge 2004;Jeffers et al. 2014;de Leon et al. 2015) extending outwards to up to 1000 au on the west side of the disk. While multiple explanations of this arm have been proposed such as a cloud remnant (Jeffers et al. 2014) or a collision with a stellar intruder (Akiyama et al. 2019), recent work by (Ginski et al. 2021) shows that, by using results reported here, the tails (both the large tail in the west and the shorter one in the north) originate from still infalling material. In Figure 12, we show the polarimetric and full intensity scattered light SPHERE data taken on the 14th of December 2019. ...
Distinguishing signal of young gas rich circumstellar disks from stellar signal in near infrared light is a difficult task. Current techniques such as Angular Differential Imaging (ADI) and Polarimetric Differential Imaging (PDI) cope with drawbacks such as self-subtraction. To address these drawbacks we explore Iterative Angular Differential Imaging (IADI) techniques to increase signal throughput in total intensity observations. This work aims to explore the effectiveness of IADI to recover the self-subtracted regions of disks by applying ADI techniques iteratively. To determine the effectiveness of IADI a model of a disk image is made and post-processed with IADI. In addition, masking based on polarimetric images and a signal threshold for feeding back signal are explored. Asymmetries are a very important factor in recovering the disk due to less overlap of the disk in the data set. In some cases, a factor 75 more flux could be recovered with IADI compared to ADI. The Procrustes distance is used to quantify the impact of the algorithm on the scattering phase function. Depending on the level of noise and the ratio between the stellar signal and disk signal, the phase function can be recovered a factor 6.4 in Procrustes distance better than standard ADI. The amplification and smearing of noise over the image due to many iterations did occur and by using binary masks and a dynamic threshold this feedback was mitigated, but it still is a problem in the final pipeline. Lastly observations of protoplanetary disks made with VLT/SPHERE were processed with IADI giving rise to very promising results. While IADI has problems with low signal-to-noise observations due to noise amplification and star reconstruction, higher signal-to-noise observations show promising results with respect to standard ADI.
... 6.5.1. This model provides good constraints on the characteristic size of the near-infrared emitting region and the flaring in the colder regions, with a sublimation temperature of 1600 K corresponding to an inner radius of 0.12 au, slightly smaller than the literature values of 0.18 ± 0.04 au (Akeson et al. 2005) and 0.17 ± 0.08 au (Jeffers et al. 2014). The disk was also found to be at an inclination of~50 • and position angle of~45 • , in agreement with both the literature and above mentioned methods. ...
... The Gaussian fitted in this work has a FWHM of 1.52 ± 0.01 mas (0.239 ± 0.002 au) at an inclination of 56.9 • ± 0.4 at a minor axis position angle of 55.9 • ± 0.5 with a stellar-to-total flux ratio of 0.57 ± 0.01. The reduced 2 value for the visibilities is 11.63 and 6.05 for the and 15 • ± 5 found by Akeson et al. (2005);Jeffers et al. (2014). This difference is likely due to either: The poor uv coverage and lack of longer baselines in previous interferometric studies, both of which make estimating the position angle and inclination particularly unreliable. ...
... The smaller grain size results in a smaller and hotter inner rim which now extends down to 0.13 au at a temperature of 2000 . This is within the uncertainties of values predicted by the temperature gradient modelling and is roughly consistent with older literature values of 0.18 ± 0.04 au and 0.17 ± 0.08 au by Akeson et al. (2005) and Jeffers et al. (2014) respectively. The flaring parameters disk and disk were fixed such that disk = disk + 1 and found to be 2.3 and 1.3 respectively. ...
A golden age of interferometry is upon us, allowing observations at smaller scales in greater detail than ever before. In few fields has this had the huge impact as that of planet formation and the study of young stars. State of the art high angular resolution observations provide invaluable insights into a host of physical processed from accretion and sublimation, to disk winds and other outflows. In this thesis, I present the wide-ranging works of my PhD, encompassing both instrumentation and observational science. Instrumentational activities stem from the development of new generation baseline solutions at CHARA to the commissioning of a new observing mode on MIRC-X, allowing for the first ever J band interferometric observations of a young stellar object ever published. The science results find direct evidence of a dusty wind emanating from the innermost regions of the young object SU Aurigae in addition to exquisite image reconstruction revealing inclination induced asymmetries. Additionally, I find evidence of viscous heating of the inner disk of outbursting star FU Orionis as I derive the temperature gradient to unparalleled precision. While it is difficult to draw one overall conclusion from the varied works of this thesis, the results described here are a testament to the uniqueness of young stellar systems and provide vital information on some the most ubiquitous processes in astrophysics. The instrumentational developments also open up exciting opportunities for future science in the ever-growing field of optical interferometry.
... Using the spectral type as well as this luminosity as input for stellar model isochrones (Siess et al. 2000), we find a stellar mass of 2.0 +0.2 −0.1 M and an age range of 4-5.5 Myr. SU Aur is surrounded by extended circumstellar structure first resolved in near infrared scattered light (Jeffers et al. 2014). The signal extends up to 500 au and shows a strong asymmetry along the East-West direction. ...
Gas-rich circumstellar disks are the cradles of planet formation. As such, their evolution will strongly influence the resulting planet population. In the ESO DESTINYS large program, we study these disks within the first 10 Myr of their development with near-infrared scattered light imaging. Here we present VLT/SPHERE polarimetric observations of the nearby class II system SU Aur in which we resolve the disk down to scales of ~7 au. In addition to the new SPHERE observations, we utilize VLT/NACO, HST/STIS and ALMA archival data. The new SPHERE data show the disk around SU Aur and extended dust structures in unprecedented detail. We resolve several dust tails connected to the Keplerian disk. By comparison with ALMA data, we show that these dust tails represent material falling onto the disk. The disk itself shows an intricate spiral structure and a shadow lane, cast by an inner, misaligned disk component. Our observations suggest that SU Aur is undergoing late infall of material, which can explain the observed disk structures. SU Aur is the clearest observational example of this mechanism at work and demonstrates that late accretion events can still occur in the class II phase, thereby significantly affecting the evolution of circumstellar disks. Constraining the frequency of such events with additional observations will help determine whether this process is responsible for the spin-orbit misalignment in evolved exoplanet systems.
... Such a reflection nebula usually seen in young stellar objects (YSOs) can be attributed to an outflow cavity as a result of stellar emission reflection at the cavity wall (e.g., Tamura et al. 1991;Lucas & Roche 1998a, 1998bPadgett et al. 1999). However, recent observations in optical and near-infrared wavelengths suggested a different origin for SU Aur, and revealed a protoplanetary disk around SU Aur and an extended tail-like structure associated with the disk (Grady et al. 2001;Chakraborty & Ge 2004;Bertout & Genova 2006;Jeffers et al. 2014;de Leon et al. 2015). Possible explanations for the origin of the tail are discussed in de Leon et al. (2015) and they suggest that tidal interaction with a brown dwarf is the the most plausible mechanism. ...
We present Atacama Large Millimeter/submillimeter Array observations of the CO (J = 2 − 1) line emission from a protoplanetary disk around T-Tauri star SU Aurigae (hereafter SU Aur). Previous observations in optical and near-infrared wavelengths find a unique structure in SU Aur. One of the highlights of the observational results is that an extended tail-like structure is associated with the disk, indicating mass transfer from or into the disk. Here we report the discovery of the counterpart of the tail-like structure in CO gas extending more than 1000 au long. Based on geometric and kinematic perspectives, both of the disk and the tail-like structure components physically connect to each other. Several theoretical studies predicted the observed tail-like structure via the following possible scenarios: (1) a gaseous stream from the molecular cloud remnant, (2) collision with a (sub)stellar intruder or a gaseous blob from the ambient cloud, and (3) ejection of a planetary or brown dwarf mass object due to gravitational instability via multibody gravitational interaction. Since the tail-like structures associated with the SU Aur disk are a new example following RW Aurigae, some disks may experience the internal or external interaction and drastically lose mass during disk evolution.
... Imaging polarimetry of SU Aur has shown that the accretion disc extends out to 500 au with an inclination of ∼50 • (Jeffers et al. 2014); the disc morphology with tidal tails was reconstructed by De Leon et al. (2015). Imaging polarimetry of RY Tau (Takami et al. 2013) showed that the scattered light in the NIR is associated with an optically thin and geometrically thick layer above the disc surface. ...
Classical T Tauri stars with ages of less than 10 Myr possess accretion discs. Magnetohydrodynamic processes at the boundary between the disc and the stellar magnetosphere control the accretion and ejections gas flows. We carried out a long series of simultaneous spectroscopic and photometric observations of the classical T Tauri stars, RY Tauri and SU Aurigae, with the aim to quantify the accretion and outflow dynamics at time-scales from days to years. It is shown that dust in the disc wind is the main source of photometric variability of these stars. In RY Tau, we observed a new effect: during events of enhanced outflow, the circumstellar extinction becomes lower. The characteristic time of changes in outflow velocity and stellar brightness indicates that the obscuring dust is near the star. The outflow activity in both stars is changing on a time-scale of years. Periods of quiescence in the variability of the Hα profile were observed during the 2015–2016 period in RY Tau and during the 2016–2017 period in SU Aur. We interpret these findings in the framework of the magnetospheric accretion model, and we discuss how the global stellar magnetic field can influence the long-term variations of the outflow activity.
... Imaging polarimetry of SU Aur has shown that the accretion disc extends out to 500 AU with an inclination of ∼ 50 • (Jeffers et al. 2014); the disc morphology with tidal tails was reconstructed by De Leon et al. (2015). Imaging polarimetry of RY Tau (Takami et al. 2013) showed that the scattered light in the near-IR is associated with an optically thin and geometrically thick layer above the disc surface. ...
Classical T Tauri stars with ages of less than 10 Myr possess accretion discs. Magnetohydrodynamic processes at the boundary between the disc and the stellar magnetosphere control the accretion and ejections gas flows. We carried out a long series of simultaneous spectroscopic and photometric observations of the classical T Tauri stars RY Tau and SU Aur with the aim to quantify the accretion and outflow dynamics at time scales from days to years. It is shown that dust in the disc wind is the main source of photometric variability of these stars. In RY Tau we observed a new effect: during events of enhanced outflow the circumstellar extinction gets lower. The characteristic time of changes in outflow velocity and stellar brightness indicates that the obscuring dust is near the star. The outflow activity in both stars is changing on a time scale of years. Periods of quiescence in H profile variability were observed during 2015-2016 season in RY Tau and during 2016-2017 season in SU Aur. We interpret these findings in the framework of the magnetospheric accretion model, and discuss how the global stellar magnetic field may influence the long-term variations of the outflow activity.
... With our broadband, visible-light imaging polarimeter ExPo [22], we have obtained many successful observations of dust structures around both young and evolved stars (e.g. [40,41,42]). ...
We present implementations of optical instrumentation that records five dimensions of light: polarization state as a function of wavelength, two spatial dimensions, and time. We focus on the optimal integration of polarimetry within microlens-based integral-field spectroscopy. The polarimetric analyzer (or beam-splitter) and dispersing element could be implemented separately, but also amalgamated in the form of a polarization grating. We present optimizations for stacking the polarization-split spectra on a 2D detector. The polarimetric modulation can be performed in the temporal, the spatial or the spectral domain. Temporal modulation could be set up with achromatic optics conform the Stokes definition scheme, but a wide wavelength range generally demands a "polychromatic" modulation approach for which the modulation efficiency for all or some of the Stokes parameters is optimized at every wavelength. Spectral modulation (full-Stokes or optimized for linear polarization) yields instruments without any moving parts, for which all polarization information is obtained in one shot. We present first results from two polarimetric IFU instruments; the ExPo pIFU and LOUPE. The first is based on a rapid polychromatic modulator consisting of two FLCs and two fixed retarders, while the latter is based on spectral modulation for linear polarization. In addition to applications within astronomy and planetary science, we discuss remote-sensing applications for such instruments.
Context. T Tauri stars are low-mass young stars whose disks provide the setting for planet formation, which is one of the most fundamental processes in astronomy. Yet the mechanisms of this are still poorly understood. SU Aurigae is a widely studied T Tauri star and here we present original state-of-the-art interferometric observations with better uv and baseline coverage than previous studies.
Aims. We aim to investigate the characteristics of the circumstellar material around SU Aur, and constrain the disk geometry, composition and inner dust rim structure.
Methods. The MIRC-X instrument at CHARA is a six-telescope optical beam combiner offering baselines up to 331 m. We undertook image reconstruction for model-independent analysis, and fitted geometric models such as Gaussian and ring distributions. Additionally, the fitting of radiative transfer models constrained the physical parameters of the disk.
Results. Image reconstruction reveals a highly inclined disk with a slight asymmetry consistent with inclination effects obscuring the inner disk rim through absorption of incident star light on the near side and thermal re-emission/scattering of the far side. Geometric models find that the underlying brightness distribution is best modelled as a Gaussian with a Full-Width Half-Maximum of 1.53 ± 0.01 mas at an inclination of 56.9 ± 0.4° and a minor axis position angle of 55.9 ± 0.5°. Radiative transfer modelling shows a flared disk with an inner radius at 0.16 au which implies a grain size of 0.14 μm assuming astronomical silicates and a scale height of 9.0 au at 100 au. In agreement with the literature, only the dusty disk wind successfully accounts for the near infrared excess by introducing dust above the mid-plane.
Conclusions. Our results confirm and provide better constraints than previous inner disk studies of SU Aurigae. We confirm the presence of a dusty disk wind in the cicumstellar environment, the strength of which is enhanced by a late infall event which also causes very strong misalignments between the inner and outer disks.
Gas-rich circumstellar disks are the cradles of planet formation. As such, their evolution will strongly influence the resulting planet population. In the ESO DESTINYS large program, we study these disks within the first 10 Myr of their development with near-infrared scattered-light imaging. Here we present VLT/SPHERE polarimetric observations of the nearby class II system SU Aur in which we resolve the disk down to scales of ∼7 au. In addition to the new SPHERE observations, we utilize VLT/NACO, HST/STIS, and ALMA archival data. The new SPHERE data show the disk around SU Aur and extended dust structures in unprecedented detail. We resolve several dust tails connected to the Keplerian disk. By comparison with ALMA data, we show that these dust tails represent material falling onto the disk. The disk itself shows an intricate spiral structure and a shadow lane, cast by an inner, misaligned disk component. Our observations suggest that SU Aur is undergoing late infall of material, which can explain the observed disk structures. SU Aur is the clearest observational example of this mechanism at work and demonstrates that late accretion events can still occur in the class II phase, thereby significantly affecting the evolution of circumstellar disks. Constraining the frequency of such events with additional observations will help determine whether this process is responsible for the spin–orbit misalignment in evolved exoplanet systems.
