J. Varga1, P. Ábrahám1, L. Chen1, Th. Ratzka2, K. É. Gabányi1, Á. Kóspál1, 3, A. Matter4, R. van Boekel3, Th. Henning3, W. Jaffe5, A. Juhász6, B. Lopez4, J. Menu7, A. Moór1, L. Mosoni1, 8, N. Sipos
Contact: József Varga, e-mail:
1 Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege Miklós út 15-17., H-1121 Budapest, Hungary; 2 Institute for Physics/IGAM, NAWI Graz, University of Graz, Universitätsplatz 5/II, 8010, Graz, Austria; 3 Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany; 4 Laboratoire Lagrange, Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Boulevard de l'Observatoire, CS 34229, 06304 Nice Cedex 4, France; 5 Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands; 6 Institute of Astronomy, Madingley Road, Cambridge CB3 OHA, UK; 7 Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001, Leuven, Belgium; 8 Park of Stars in Zselic, 064/2 hrsz., H-7477 Zselickisfalud, Hungary
Links to the paper: ArXiv, ADS.
This atlas presents mid-infrared interferometric spectra of 82 low- and intermediate-mass young stellar objects (YSOs). The data were taken from the archive of the Mid-infrared Interferometric Instrument (MIDI, Leinert et al., 2003) on the Very Large Telescope Interferometer (VLTI). Our sample contains 82 objects, of which 45 are T Tauri stars, 11 are young eruptive stars, and 26 are Herbig Ae stars. Observation dates range from 2003 to 2015. We homogeneously reduced and calibrated the interferometric data using the Expert Work Station (EWS) package 2.0 software. The atlas contains correlated spectra, total spectra, squared visibilities, and differential phases in the 7.5 - 13 μm wavelength range. Data between 9.4 and 10.0 μm can be heavily affected by the atmospheric ozone absorption feature, especially in the total spectra.
Context. Protoplanetary disks show large diversity regarding their morphology and dust composition. With mid-infrared interferometry the thermal emission of disks can be spatially resolved, and the distribution and properties of the dust within can be studied.
Aims. Our aim is to perform a statistical analysis on a large sample of 82 disks around low- and intermediate-mass young stars, based on mid-infrared interferometric observations. We intend to study the distribution of disk sizes, variability and the silicate dust mineralogy.
Methods. Archival mid-infrared interferometric data from the VLTI/MIDI instrument are homogeneously reduced and calibrated. Geometric disk models are used to fit the observations to get spatial information about the disks. An automatic spectral decomposition pipeline is applied to analyze the shape of the silicate feature.
Results. We present the resulting data products in the form of an atlas, containing N band correlated and total spectra, visibilities and differential phases. Majority of our data can be well fitted with a continuous disk model, except for a few objects, where a gapped model gives a better match. From the mid-infrared size - luminosity relation we find, that disks around T Tauri stars are generally colder and more extended with respect to the stellar luminosity, than disks around Herbig Ae stars. We find that in the innermost part of the disks (r < 1 au) the silicate feature is generally weaker than in the outer parts, suggesting that in the inner parts the dust is substantially more processed. We analyze stellar multiplicity and find that in 2 systems (AB Aur, HD 72106) data suggest a new companion or asymmetric inner disk structure. We made predictions for the observability of our objects with the upcoming MATISSE instrument, supporting the practical preparations of future MATISSE observations of T Tauri stars.
We modeled the interferometric data using a simple geometry to describe
the brightness distribution of the disks. The geometry of our model is a thin, flat, face-on disk, beginning at the dust sublimation radius (Rsub), and extending to Rout = 300 au, where the mid-IR radiation is already negligible. The disk emits blackbody radiation with a temperature decreasing as a power-law:
T(R) = Tsub(R/Rsub)-q
Tsub is the dust sublimation temperature, fixed at 1500 K.
Rsub is calculated from the luminosity and distance of the central star. The fitted parameters are the temperature power-law exponent q, and the total flux Ftot,ν. From q a half-light radius (rhl) is calculated. This model is shown as solid line in the plots.
Because inner gaps are common features of circumstellar disks, we also try to reproduce the data with a second model where the inner radius (Rin) is a free parameter. Thus this model can fit disks with gaps. The other parameter of the model is q. Ftot,ν is calculated as the median of the total fluxes.
Each figure have three panels. Data taken with the UTs and ATs are marked with circles and diamonds, respectively. Top panel: uv-coverage plot. Data shown with small symbols are flagged as unreliable. Middle panel: Gaussian size diagram. The plot shows the physical sizes of the disk (HWHM, in au) individually measured for each observations corresponding to different baseline angles. Bottom panel: Results of the interferometric modeling to the correlated and total fluxes (shown at 0 m baseline) at 10.7 μm as a function of projected baseline length. Blue solid line: continuous model fit. Blue dashed line: gapped model fit. Red and green lines show the correlated fluxes extrapolated from the continuous model to the K and L bands, respectively. Dotted lines show the estimates for the unresolved stellar emission. Data points on each subplot are color coded for observation date.
These figures show the calibrated MIDI spectra, generated by the data reduction pipeline (MIA+EWS, using the python wrapper code of Menu et al., 2015).
Correlated spectra.
Total spectra.
Visibilities.
Differential phases.
One of the aims of this atlas is to provide an input database for the MATISSE instrument (Lopez et al. 2014, Matter et al. 2016a), from which one can derive the observability of the objects depending on the wavelength and the baseline length. With an extrapolation of our interferometric modeling of N band MIDI observations, we estimated K and L band correlated fluxes for 15, 30, 60, 100, 130, and 150 m projected baseline lengths for all sources in the sample. Total fluxes are also estimated. Each observability plot has three panels: top panel shows L versus N band, middle panel shows K versus N band, and bottom panel shows K versus L band fluxes. The color of the symbols indicates the object type: Herbig Ae (blue), T Tauri (red), and eruptive systems (orange). Vertical solid and dashed lines indicate the expected MATISSE N or L band sensitivity limits with or without using an external fringe tracker, respectively. Blue and red lines represent the sensitivity limits with ATs and UTs, respectively. Horizontal dashed lines indicate the K sensitivity limits of the external fringe tracker with ATs or UTs (in the middle and bottom panels). In the top panel, horizontal lines indicate the L band sensitivity limits. Sources in the green shaded area can be observed either with the UTs and ATs, objects in the orange shaded region can only be observed with UTs. Flux limits were taken from Matter et al., 2016b.
Data are presented in OIFITS version 2 format (Duvert et al., 2017). The OIFITS files contain all spectra in all epochs for each object: the OI_VIS2 table contains the squared visibilities, the OI_VIS table contains the correlated spectra (VISAMP column, Jy) and the differential phases (VISPHI column, deg), and the OI_FLUX table contains the total spectra (Jy). Additionally, we present here the three tables from the paper in machine-readable csv files: table1.csv contains the overview of the sample with basic stellar parameters (= Table 1 in the paper), table2.csv lists the results of the interferometric modeling of the objects (= Table 2 in the paper), and tableE1.csv lists of all MIDI interferometric observations presented in the atlas (= Table E1 in the paper). The first line of the csv files contains the column labels and the second line contains the units. References cited in table1.csv are listed in the refs.csv file with their bibcodes.