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Register a new userConstraining the Sub-AU-Scale Distribution of Hydrogen and Carbon Monoxide Gas around Young Stars with the Keck Interferometer
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We present Keck Interferometer observations of T Tauri and Herbig Ae/Be stars with a spatial resolution of a few milliarcseconds and a spectral resolution of ~2000. Our observations span the K-band, and include the Br gamma transition of Hydrogen and the v=2-0 and v=3-1 transitions of carbon monoxide. For several targets we also present data from Keck/NIRSPEC that provide higher spectral resolution, but a seeing-limited spatial resolution, of the same spectral features. We analyze the Br gamma emission in the context of both disk and infall/outflow models, and conclude that the Br gamma emission traces gas at very small stellocentric radii, consistent with the magnetospheric scale. However some Br gamma-emitting gas also seems to be located at radii of >0.1 AU, perhaps tracing the inner regions of magnetically launched outflows. CO emission is detected from several objects, and we generate disk models that reproduce both the KI and NIRSPEC data well. We infer the CO spatial distribution to be coincident with the distribution of continuum emission in most cases. Furthermore the Br gamma emission in these objects is roughly coincident with both the CO and continuum emission. We present potential explanations for the spatial coincidence of continuum, Br gamma, and CO overtone emission, and explore the implications for the low occurrence rate of CO overtone emission in young stars. Finally, we provide additional discussion of V1685 Cyg, which is unusual among our sample in showing large differences in emitting region size and spatial position as a function of wavelength.
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We present Keck Interferometer observations of the three prototypical FU Orionis stars, FU Ori, V1057 Cyg, and V1515 Cyg. With a spatial resolution of a few milli-arcseconds and a spectral resolution of 2000, our near-infrared observations spatially resolve gas and dust emission extending from stellocentric radii of ~0.05 AU to several AU. We fit these data with accretion disk models where each stellocentric radius of the disk is represented by a supergiant-type stellar emission spectrum at the disk temperature. A disk model is consistent with the data for FU Ori, although we require some local asymmetry in the disk. For V1057 Cyg the disk model does not fit our data well, especially compared to the fit quality achieved for FU Ori. We speculate that a disk wind may be contributing substantially to the observed near-IR emission in this source. The data for V1515 Cyg are noisier than the data obtained for the other two objects, and do not strongly constrain the validity of an accretion disk model.
The relationship between young stellar clusters and respective parental molecular clouds is still an open issue: for instance, are the similarities between substructures of clouds and clusters just a coincidence? Or would they be the indication of a physical relationship? In order to address these issues, we have studied the CMa OB1/R1 region that shows evidence for a complex star formation history. We obtained molecular clouds mapping with the IRAM-30 metre telescope to reveal the physical conditions of an unexplored side of the CMa region aiming to compare the morphology of the clouds with the distribution of the young stellar objects (YSOs). We also study the clouds kinematics searching for gradients and jet signatures that could trace different star formation scenarios. The YSOs were selected on the basis of astrometric data from Gaia EDR3 that characterise the moving groups. The distance of 1099$_{-24}^{+25}$ pc was obtained for the sample, based on the mean error-weighted parallax. Optical and near-infrared photometry is used to verify the evolutionary status and circumstellar characteristics of the YSOs. Among the selected candidates we found 40 members associated with the cloud: 1 Class I, 11 Class II, and 28 Class III objects. Comparing the spatial distribution of the stellar population with the cores revealed by the 13CO map, we verify that peaks of emission coincide with the position of YSOs confirming the association of these objects to their dense natal gas. Our observations support the large-scale scenario of the CMa shell-like structure formed as a relic of successive supernova events.
We report the detection of carbon monoxide (CO) emission from the young supernova remnant Cassiopeia A (Cas A) at wavelengths corresponding to the fundamental vibrational mode at 4.65 micron. We obtained AKARI Infrared Camera spectra towards 4 positions which unambiguously reveal the broad characteristic CO ro-vibrational band profile. The observed positions include unshocked ejecta at the center, indicating that CO molecules form in the ejecta at an early phase. We extracted a dozen spectra across Cas A along the long 1 arcmin slits, and compared these to simple CO emission models in Local Thermodynamic Equilibrium to obtain first-order estimates of the excitation temperatures and CO masses involved. Our observations suggest that significant amounts of carbon may have been locked up in CO since the explosion 330 years ago. Surprisingly, CO has not been efficiently destroyed by reactions with ionized He or the energetic electrons created by the decay of the radiative nuclei. Our CO detection thus implies that less carbon is available to form carbonaceous dust in supernovae than is currently thought and that molecular gas could lock up a significant amount of heavy elements in supernova ejecta.
HD 50138 is a B[e] star surrounded by a large amount of circumstellar gas and dust. Its spectrum shows characteristics which may indicate either a pre- or a post-main-sequence system. Mapping the kinematics of the gas in the inner few au of the system contributes to a better understanding of its physical nature. We present the first high spatial and spectral resolution interferometric observations of the Br-gamma line of HD~50138, obtained with VLTI/AMBER. The line emission originates from a region more compact (up to 3 au) than the continuum-emitting region. Blue- and red-shifted emission originates from the two different hemispheres of an elongated structure perpendicular to the polarization angle. The velocity of the emitting medium decreases radially. An overall offset along the NW direction between the line- and continuum-emitting regions is observed. We compare the data with a geometric model of a thin Keplerian disk and a spherical halo on top of a Gaussian continuum. Most of the data are well reproduced by this model, except for the variability, the global offset and the visibility at the systemic velocity. The evolutionary state of the system is discussed; most diagnostics are ambiguous and may point either to a post-main-sequence or a pre-main-sequence nature.
The hydrogen cyanide (HCN) molecule in the planetary atmosphere is key to the formation of building blocks of life. We present the spectroscopic detection of the rotational molecular line of nitrile species hydrogen cyanide (HCN) in the atmosphere of Saturn using the archival data of the Atacama Large Millimeter/Submillimeter Array (ALMA) in band 7 observation. The strong rotational emission line of HCN is detected at frequency $ u$ = 354.505 GHz (>4$sigma$ statistical significance). We also detect the rotational emission line of carbon monoxide (CO) at frequency $ u$ = 345.795 GHz. The statistical column density of hydrogen cyanide and carbon monoxide emission line is N(HCN)$sim$2.42$times$10$^{16}$ cm$^{-2}$ and N(CO)$sim$5.82$times$10$^{17}$ cm$^{-2}$. The abundance of HCN and CO in the atmosphere of Saturn relative to the H$_{2}$ is estimated to be f(HCN)$sim$1.02$times$10$^{-9}$ and f(CO)$sim$2.42$times$10$^{-8}$. We discussed possible chemical pathways to the formation of the detected nitrile gas HCN in the atmosphere of Saturn.
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