Infrared excesses in stars with and without planets using revised WISE{\it WISE} photometry

We present an analysis on the potential prevalence of mid infrared excesses in stars with and without planetary companions. Based on an extended database of stars detected with the ${\it WISE}$ satellite, we studied two stellar samples: one with 236 planet hosts and another with 986 objects for which planets have been searched but not found. We determined the presence of an excess over the photosphere by comparing the observed flux ratio at 22 $\mu$m and 12 $\mu$m ($f_{22}/f_{12}$) with the corresponding synthetic value, derived from results of classical model photospheres. We found a detection rate of 0.85$\%$ at 22 $\mu$m (2 excesses) in the sample of stars with planets and 0.1$\%$ (1 detection) for the stars without planets. The difference of the detection rate between the two samples is not statistically significant, a result that is independent of the different approaches found in the literature to define an excess in the wavelength range covered by ${\it WISE}$ observations. As an additional result, we found that the ${\it WISE}$ fluxes required a normalisation procedure to make them compatible with synthetic data, probably pointing out a revision of the ${\it WISE}$ data calibration.Comment: 10 pages, 6 figures, 3 tables. Accepted for publication in MNRA

Massive compact disks around FU Orionis-type young eruptive stars revealed by ALMA

FU Orionis-type objects (FUors) are low-mass pre-main sequence stars undergoing a temporary, but significant increase of mass accretion rate from the circumstellar disk onto the protostar. It is not yet clear what triggers the accretion bursts and whether the disks of FUors are in any way different from disks of non-bursting young stellar objects. Motivated by this, we conducted a 1.3 mm continuum survey of ten FUors and FUor-like objects with ALMA, using both the 7 m array and the 12 m array in two different configurations to recover emission at the widest possible range of spatial scales. We detected all targeted sources and several nearby objects as well. To constrain the disk structure, we fit the data with models of increasing complexity from 2D Gaussian to radiative transfer, enabling comparison with other samples modeled in a similar way. The radiative transfer modeling gives disk masses that are significantly larger than what is obtained from the measured millimeter fluxes assuming optically thin emission, suggesting that the FUor disks are optically thick at this wavelength. In comparison with samples of regular Class II and Class I objects, the disks of FUors are typically a factor of 2.9-4.4 more massive and a factor of 1.5-4.7 smaller in size. A significant fraction of them (65-70%) may be gravitationally unstable

APEX Observations of the CO Envelope around the Young FUor-type Star V883 Ori

The accretion-driven outbursts of young FU Orionis–type stars may be a common stage of pre-main-sequence evolution and can have a significant impact on the circumstellar environment as it pertains to the growth of solids and eventually planets. This episodic accretion is thought to be sustained by additional gas infalling from the circumstellar envelope and disk. We present APEX observations of the CO gas in the envelope around V883 Orionis, a young outbursting star. The observations mapped the 12CO(4–3), 12CO(3–2), and 13CO(3–2) lines with the FLASH+ instrument and the 12CO(6–5) line with the SEPIA instrument. We detected high signal-to-noise emission extending out to radii >10,000 au and calculated integrated fluxes of 1100 Jy km s‑1 for 12CO(6–5), 2400 Jy km s‑1 for 12CO(4–3), 1600 Jy km s‑1 for 12CO(3–2), and 450 Jy km s‑1 for 13CO(3–2). We used the thermochemical code PRODIMO to test several models and find the data are best described by an envelope structure with M env ≈ 0.2–0.4 M ⊙ and a mass-infall rate of {\\dot{M}}\\inf =1{--}2× {10}-6 {M}ȯ {yr}}-1. We infer that the observed envelope and outflow structure around V883 Ori could be caused by multiple outbursts, consistent with episodic accretion

The Relation between the Mass Accretion Rate and the Disk Mass in Class I Protostars

Evidence of a relation between the mass accretion rate and the disk mass is established for young, Class II pre-main-sequence stars. This observational result opened an avenue to test theoretical models and constrain the initial conditions of disk formation, fundamental in the understanding of the emergence of planetary systems. However, it is becoming clear that planet formation starts even before the Class II stage, in disks around Class 0 and I protostars. We show for the first time evidence for a correlation between the mass accretion rate and the disk mass for a large sample of Class I young stars located in nearby (<500 pc) star-forming regions. We fit our sample, finding that the Class I object relation has a slope flatter than Class II stars, and the former have higher mass accretion rates and disk masses. The results are put in context of disk evolution models

ALMA and VLA Observations of EX Lupi in Its Quiescent State

Extreme outbursts in young stars may be a common stage of pre-main-sequence stellar evolution. These outbursts, caused by enhanced accretion and accompanied by increased luminosity, can also strongly impact the evolution of the circumstellar environment. We present Atacama Large Millimeter Array (ALMA) and Very Large Array observations of EX Lupi, a prototypical outburst system, at 100, 45, and 15 GHz. We use these data, along with archival ALMA 232 GHz data, to fit radiative transfer models to EX Lupi's circumstellar disk in its quiescent state following the extreme outburst in 2008. The best-fit models show a compact disk with a characteristic dust radius of 45 au and a total mass of 0.01 M☉. Our modeling suggests grain growth to sizes of at least 3 mm in the disk, possibly spurred by the recent outburst, and an ice line that has migrated inward to 0.2-0.3 au post-outburst. At 15 GHz, we detected significant emission over the expected thermal disk emission which we attribute primarily to stellar (gyro)synchrotron and free-free disk emission. Altogether, these results highlight what may be a common impact of outbursts on the circumstellar dust

An ALMA Study of the FU Ori─type Object V900 Mon: Implications for the Progenitor

We present ALMA observations of 12CO, 13CO, and C18O J = 2─1 lines and the 230 GHz continuum for the F Ori─type object (FUor) V900 Mon (d ∼ 1.5 kpc), for which the accretio burst was triggered between 1953 and 2009. We identified CO emissio associated with a molecular bipolar outflow extending up to a ∼104 au scale and a rotating molecular envelope extendin over >104 au. The interaction with the hot energetic FUo wind, which was observed using optical spectroscopy, appears limited t a region within ∼400 au of the star. The envelope mass and collimatio of the extended CO outflow suggest that the progenitor of this FUor is low-mass Class I young stellar object (YSO). These parameters for V90 Mon, another FUor, and a few FUor-like stars are consistent with th idea that FUor outbursts are associated with normal YSOs. The continuu emission is marginally resolved in our observations with a 0.″2 × 0.″1 (∼300 × 225 au) beam, and a Gaussian model provides a deconvolved FWH of ∼90 au. The emission is presumably associated with a dust circumstellar disk, plus a possible contribution from a wind or win cavity close to the star. The warm compact nature of the disk continuu emission could be explained with viscous heating of the disk, whil gravitational fragmentation in the outer disk and/or a combination o grain growth and their inward drift may also contribute to its compac nature

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