FU Orionis objects are a class of young stars with powerful bursts in
luminosity that show evidence of accretion and ejection activity. It is
generally accepted that they are surrounded by a Keplerian circumstellar
disk and an infalling envelope. The outburst occurs because of a sudden
increase in the accretion rate through the disk. In this scenario, all
young stars experience FU Ori phases during their evolution. Despite the
evidence of winds/outflows and accretion activity in these objects, a
detailed study of their physical properties has been difficult to carry
out with high-resolution instruments manly due to the faintness and the
distance to these objects.
Using the integral field spectrograph OASIS, at the William Herschel
Telescope, combined with the adaptive optics module NAOMI, astronomers
obtained optical observations of the FU Ori star V1515 Cyg with an
angular resolution of 0.7 arcseconds (Gaussian core FWHM). From the
analysis of the data they find evidence for the existence of a
surrounding disk in V1515, being this one of the few spatial inferences
of a disk observed in an FU Ori object.
They applied a spectro-astrometry technique to both spatial directions. A
two-dimensional circular Gaussian was fitted to each image of the data
cube, with a Levenberg-Marquardt algorithm. The wavelength-dependent
Gaussian centers and Gaussian full width at half maximum (FWHM) are the
spectro-astrometric signal. Figure 1 shows, for one of the individual
exposures, the detected spectro-astrometric signal in the spatial
directions for the spectral region around the Hα 6562Å line. A small
spectro-astrometric signal is detected in the horizontal direction.
However, considering the error bars, the signal in the vertical
direction is clearly detected at blueshifted velocities of ∼-100 km s-1.
In order to ruled out the possibility of a bias due to a deficient
wavelength calibration, a model fitting between each spectrum in the
field and the one at the stellar position was carried out. The top panel
in Figure 2 shows the spatially distribution of the measured shift for
the same exposures as in Figure 1. A clear structure is seen in the
center of the field with an approximate size of ∼2 arcseconds in both
spatial directions.
The astronomers identify two clear distinct regions, one showing
redshifted velocities and the other blueshifted, almost symmetrical to
the previous one.
This structure, similar to 12CO observations in several T Tauri stars suggests scattering coming from a disk surrounding the star.
Top: shift in velocity obtained from a cross-correlation of the P Cygni
profile between the spectrum at the position of the star and each
individual spectra in the field, for exposure 1. Color scale is km s-1.
The continuum emission center is marked as a black cross. The physical
orientation is also given. Bottom: error in the shift also in km s-1 [ PNG ]
More information:
V. Agra-Amboage and P. J. V. Garcia, 2014, "Spectro-astrometry of V1515 Cygni", A&A, 565, A92. Paper.
Contact:
Javier Méndez
(Public Relations Officer)
Source: Isaac Newton Group of Telescopes
