Spectro-astrometry: The Method, its Limitations, and Applications

Whelan, Emma; Garcia, Paulo J. V.

doi:10.1007/978-3-540-68032-1_6

Cited by 44 publications

(48 citation statements)

References 34 publications

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“…We note that the recommended procedure to calibrate the spectroastrometric signals requires observations with parallel and anti-parallel slit position angles (Brannigan et al 2006). Since the archival CRIRES data lack anti-parallel position angles, we limit our analysis to the following: Spectroastrometry tracks the centroid of the stellar continuum and of the emission line as a function of wavelength, with an astrometric precision of the order of few milliarcseconds (see Whelan & Garcia 2008). The SA signal was measured on the non-continuum-subtracted data, and recovered by applying a Gaussian fitting to the intensity profile of the observed lines along the spatial axis for each one of the dispersion axis bins.…”

Section: The H 2 and Brγ Spectroastrometric Signalsmentioning

confidence: 99%

Unveiling the near-infrared structure of the massive-young stellar object NGC 3603 IRS 9A* with sparse aperture masking and spectroastrometry

Sánchez-Bermúdez

Hummel

Tuthill

et al. 2016

A&A

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Context. Contemporary theory holds that massive stars gather mass during their initial phases via accreting disk-like structures. However, conclusive evidence for disks has remained elusive for most massive young objects. This is mainly due to significant observational challenges: objects are rare and located at great distances within dusty, highly opaque environments. Incisive studies, even targeting individual objects, are therefore relevant to the progression of the field. NGC 3603 IRS 9A* is a young massive stellar object that is still surrounded by an envelope of molecular gas for which previous mid-infrared observations with long-baseline interferometry have provided evidence of a plausible disk of 50 mas diameter at its core. Aims. This work aims at a comprehensive study of the physics and morphology of IRS 9A at near-infrared wavelengths. Methods. New sparse aperture-masking interferometry data, taken with the near-infrared camera NACO of the Very Large Telescope (VLT) at K s and L wavelengths, were analyzed together with archival high-resolution H 2 and Brγ lines obtained with the cryogenic high-resolution infrared schelle spectrograph (CRIRES). Results. The trends in the calibrated visibilities at K s and L -bands suggest the presence of a partially resolved compact object with an angular size of ≤30 mas at the core of IRS 9A, together with the presence of over-resolved flux. The spectroastrometric signal of the H 2 line, obtained from the CRIRES spectra, shows that this spectral feature proceeds from the large-scale extended emission (∼300 mas), while the Brγ line appears to be formed at the core of the object (∼20 mas). To better understand the physics that drive IRS 9A, we have performed continuum radiative transfer modeling. Our best model supports the existence of a compact disk with an angular diameter of 20 mas, together with an outer envelope of 1 exhibiting a polar cavity with an opening angle of ∼30 • . This model reproduces the MIR morphology that has previously been derived in the literature and also matches the spectral energy distribution (SED) of the source. Conclusions. Our observations and modeling of IRS 9A support the presence of a disk at the core, surrounded by an envelope. This scenario is consistent with the brightness distribution (SED) of the source for near-and mid-infrared wavelengths at various spatial scales. However, our model suffers from remaining inconsistencies between SED modelling and the interferometric data. Moreover, the Brγ spectroastrometric signal indicates that the core of IRS 9A exhibits some form of complexity such as asymmetries in the disk. Future high-resolution observations are required to confirm the disk/envelope model and to flesh out the details of the physical form of the inner regions of IRS 9A.

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Section: The H 2 and Brγ Spectroastrometric Signalsmentioning

confidence: 99%

Unveiling the near-infrared structure of the massive-young stellar object NGC 3603 IRS 9A* with sparse aperture masking and spectroastrometry

Sánchez-Bermúdez

Hummel

Tuthill

et al. 2016

A&A

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“…However, such observations are very time consuming and difficult to reduce. The method is described in detail in Whelan & Garcia (2008) and I introduce only some basic quantities and example applications here. Figure 11 illustrates the basic concept.…”

Section: Spectro-astrometrymentioning

confidence: 99%

Modeling and interpretation of line observations

Kamp

2015

EPJ Web of Conferences

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Abstract. Models for the interpretation of line observations from protoplanetary disks are summarized. The spectrum ranges from 1D LTE slab models to 2D thermo-chemical radiative transfer models and their use depends largely on the type/nature of observational data that is analyzed. I discuss the various types of observational data and their interpretation in the context of disk physical and chemical properties. The most simple spatially and spectral unresolved data are line fluxes, which can be interpreted using so-called Boltzmann diagrams. The interpretation is often tricky due to optical depth and non-LTE effects and requires care. Line profiles contain kinematic information and thus indirectly the spatial origin of the emission. Using series of line profiles, we can for example deduce radial temperature gradients in disks (CO pure rotational ladder). Spectro-astrometry of e.g. CO ro-vibrational line profiles probes the disk structure in the 1-30 AU region, where planet formation through core accretion should be most efficient. Spatially and spectrally resolved line images from (sub)mm interferometers are the richest datasets we have to date and they enable us to unravel exciting details of the radial and vertical disk structure such as winds and asymmetries. The power of line observationsThere are two main goals in observing line emission: (1) to obtain a chemical inventory in space and (2) to learn about the physical conditions in astrophysical environments. An example of the first is the HEXOS program, a Herschel/HIFI key program lead by E.A. Bergin, which besides other goals aims at a chemical inventory of the Orion and Sagittarius B2 star forming regions. They identified complex organic species such as methanol (CH 3 OH), methyl formate (CH 3 OCHO) and dimethyl-ether (CH 3 OCH 3 ) as well as hydrogen cyanide (HCN) and methyl cyanide (CH 3 CN), which are thought to be pre-cursors of amino acids (Crockett et al. 2014). An example for learning about physical conditions are the fine structure and molecular lines observed towards the dark cloud core Barnard 5 (Bensch 2006). Comparing the line ratio [C i]/CO J=3-2 with 1D spherical PDR models allows to estimate the total mass and density of the region close to the central core.Molecular spectra with their wealth of lines tracing different excitation conditions (rotational, vibrational, electronic) are excellent tracers of gas densities, temperatures and kinematics over a wide variety of environments in disks (see chapter by Dionatos 2015). However, disks are complicated three-dimensional structures, in which different molecular lines originate from different regions (radial and vertical) Article available at

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“…As the most intense forbidden emission coincides with the critical density region it is currently challenging to directly resolve a BD outflow in FELs and this goal has not yet been achieved. Our approach to this problem has been to obtain high quality spectra using the UV-Visual Echelle Spectrometer (UVES) on the European Southern Observatory's (ESO) Very Large Telescope (VLT) and to recover the spatial offset in the region of forbidden emission using spectro-astrometry (Whelan & Garcia 2008).…”

Section: Brown Dwarf Outflowsmentioning

confidence: 99%

Brown dwarf jets: Investigating the universality of jet launching mechanisms at the lowest masses

et al. 2010

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Abstract.Recently it has become apparent that proto-stellar-like outflow activity extends to the brown dwarf (BD) mass regime. While the presence of accretion appears to be the common ingredient in all objects known to drive jets fundamental questions remain unanswered. The more prominent being the exact mechanism by which jets are launched, and whether this mechanism remains universal among such a diversity of sources and scales. To address these questions we have been investigating outflow activity in a sample of protostellar objects that differ considerably in mass and mass accretion rate. Central to this is our study of brown dwarf jets. To date Classical T Tauri stars (CTTS) have offered us the best touchstone for decoding the launching mechanism. Here we shall summarise what is understood so far of BD jets and the important constraints observations can place on models. We will focus on the comparison between jets driven by objects with central mass < 0.1M and those driven by CTTSs. In particular we wish to understand how the the ratio of the mass outflow to accretion rate compares to what has been measured for CTTSs.

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Spectro-astrometry: The Method, its Limitations, and Applications

Cited by 44 publications

References 34 publications

Unveiling the near-infrared structure of the massive-young stellar object NGC 3603 IRS 9A* with sparse aperture masking and spectroastrometry

Unveiling the near-infrared structure of the massive-young stellar object NGC 3603 IRS 9A* with sparse aperture masking and spectroastrometry

Modeling and interpretation of line observations

Brown dwarf jets: Investigating the universality of jet launching mechanisms at the lowest masses

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