J/A+A/639/A121 LkCa 15 and 2MASS J16100501-2132318 ALMa images (Facchini+, 2020)
Annular substructures in the transition disks around LkCa 15 and J1610.
Facchini S., Benisty M., Bae J., Loomis R., Perez L., Ansdell M., Mayama S.,
Pinilla P., Teague R., Isella A., Mann A.
<Astron. Astrophys. 639, A121 (2020)>
=2020A&A...639A.121F 2020A&A...639A.121F (SIMBAD/NED BibCode)
ADC_Keywords: Stars, pre-main sequence ; Radio sources
Keywords: accretion, accretion disks - planetary systems: protoplanetary disks -
stars: individual: LkCa15 -
stars: individual: 2MASS J16100501-2132318 -
submillimeter: planetary systems
Abstract:
We present high-resolution millimeter continuum ALMA observations of
the disks around the T Tauri stars LkCa 15 and 2MASS J16100501-2132318
(hereafter, J1610). These transition disks host dust-depleted inner
regions, which have possibly been carved by massive planets, and they
are of prime interest to the study of the imprints of planet-disk
interactions. While at moderate angular resolution, they appear as a
broad ring surrounding a cavity, the continuum emission resolves into
multiple rings at a resolution of ∼60x40,mas (∼7.5au for LkCa 15, ∼6au
for J1610) and ∼7uJy/beam rms at 1.3mm. In addition to a broad
extended component, LkCa 15 and J1610 host three and two narrow rings,
respectively, with two bright rings in LkCa 15 being radially
resolved. LkCa 15 possibly hosts another faint ring close to the outer
edge of the mm emission. The rings look marginally optically thick,
with peak optical depths of ∼0.5 (neglecting scattering), in agreement
with high angular resolution observations of full disks. We performed
hydrodynamical simulations with an embedded, sub-Jovian-mass planet
and show that the observed multi-ringed substructure can be
qualitatively explained as the outcome of the planet-disk interaction.
We note, however, that the choice of the disk cooling timescale alone
can significantly impact the resulting gas and dust distributions
around the planet, leading to different numbers of rings and gaps and
different spacings between them. We propose that the massive outer
disk regions of transition disks are favorable places for
planetesimals, and possibly second-generation planet formation of
objects with a lower mass than the planets carving the inner cavity
(typically few MJup), and that the annular substructures observed in
LkCa∼15 and J1610 may be indicative of planetary core formation within
dust-rich pressure traps. Current observations are compatible with
other mechanisms contributing to the origin of the observed
substructures, in particular with regard to narrow rings generated (or
facilitated) at the edge of the CO and N2 snowlines.
Description:
ALMA Band 6 observations of LkCa 15 and 2MASS J16100501-2132318
(J1610), Program #2018.1.01255.S. The observations were carried out
with different configurations in order to provide good uv-coverage at
different spatial frequencies, using nominal C43-5, C43-8 and C43-9
configurations for LkCa 15, and C43-6 and C43-8 for J1610. The
spectral setup of the imaged data had 3 spws with central rest
frequency of 214, 216.2 and 229GHz. The data were calibrated using the
CASA package, version 5.6. Self-calibration was performed on all
data-sets, leading to a good improvement in the signal-to-noise (S/N)
ratio.The visibilities were merged using the concat task in CASA, and
spectrally re-binned on 250MHz channels to avoid bandwidth smearing.
Images in the sky plane were produced using the tclean task, with the
multiscale cleaning algorithm allowing for point source emission.
Elliptical masks were applied, with position angle and inclination
derived from (u,v)-plane analysis, and a semi-major axis of 1.7" and
1" for LkCa 15 and J1610, respectively. The de-convolution was
performed down to a cleaning threshold of 1σ, which maximises
the flux in the clean model. The residuals in the final images were
rescaled by the ratio of the clean beam and dirty beam (Jorsater & van
Moorsel 1995), which reduced the rms noise level by ∼50%. This is to
correct for the fact that the final image is the sum of the restored
clean components (in units of clean beams) and of the residuals (in
units of dirty beams); to properly estimate the flux of the residuals,
a re-normalization factor equal to the ratio of the two beam areas is
applied to them. Different weighting schemes were tested to produce
the images. The best compromise between angular resolution and S/N for
LkCa 15 is with a Briggs robust weighting of 0, whereas for J1610 we
opted for a Briggs robust weighting of 0.3. The resulting synthesized
beam for LkCa 15 is 68x47mas, with a position angle (P.A.) of
347.4°. The rms noise level is ∼6.9uJy/beam, as estimated from an
annulus centered in the phase center with a 2.5-4" range in radii, and
the image has a signal-to-noise (S/N) ratio of ∼115 at the peak. For
J1610, the synthesized beam is 55x43mas with a P.A. of 50.3°, and
the rms noise level is ∼7.2uJy/beam. The S/N at the peak is ∼75. The
recovered flux density within the cleaning mask is 136.4=/-0.1mJy and
30.8±0.1mJy for LkCa 15 and J1610, respectively.
Objects:
----------------------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------------------
04 39 17.79 +22 21 03.4 LkCa 15 = EM* LkCa
16 10 05.02 -21 32 31.9 J1610 = 2MASS J16100501-2132318
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 159 2 List of fits images
fits/* . 2 Individual fits images
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 55 A26 "datime" Obs.date Observation date
57- 63 F7.3 GHz Freq Observed frequency
65- 68 I4 Kibyte size Size of FITS file
70-117 A48 --- FileName Name of FITS file, in subdirectory fits
119-159 A41 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Stefano Facchini, stefano.facchini(at)eso.org
(End) Patricia Vannier [CDS] 29-May-2020