We argue that the periodic variability of Class II methanol masers can be explained by variations of the dust temperature in the accretion disk around proto-binary star with at least one massive component. The dust temperature variations are caused by rotation of hot and dense material of the spiral shock wave in the disk central gap. The aim of this work is to show how different can be the Class II methanol maser brightness in the disk during the M oment of M aximum I llumination by the S piral S hock material (hereafter MMISS) and the M oment when the disk is I lluminated by the S tars O nly (MISO). We used the code CLOUDY (v13.02) to estimate physical conditions in the flat disk in the MISO and the MMISS. Model physical parameters of the disk were then used to estimate the brightness of 6.7, 9.9, 12.1 and 107 GHz masers at different impact parameters p using LVG approximation. It was shown that the strong masers experience considerable brightness increase during the MMISS with respect to MISO. There can happen both flares and dips of the 107 GHz maser brightness under the MMISS conditions, depending on the properties of the system.

The formation of asteroids, comets, and planets occurs in the interior of protoplanetary disks during the early phase of star formation. Consequently, the chemical composition of the disk might shape the properties of the emerging planetary system. In this context, it is crucial to understand whether and what organic molecules are synthesized in the disk. In this Letter, we report the first detection of formic acid (HCOOH) toward the TW Hydrae protoplanetary disk. The observations of the trans-HCOOH 6 (1,6)-5(1,5) transition were carried out at 129 GHz with Atacama Large Millimeter/Submillimeter Array (ALMA). We measured a disk-averaged gas-phase t-HCOOH column density of ∼(2-4)×10 12 cm −2 , namely as large as that of methanol. HCOOH is the first organic molecule containing two oxygen atoms detected in a protoplanetary disk, a proof that organic chemistry is very active, albeit difficult to observe, in these objects. Specifically, this simplest acid stands as the basis for synthesis of more complex carboxylic acids used by life on Earth.

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We present astrometric analysis of archival data of water masers in the starforming region Sharpless 269 (S269) IRS 2w, observed with the VLBI Exploration of Radio Astrometry. An annual parallax of one of the bright maser features in this region was previously reported to be 0.189 ± 0.008 milliarcsecond (mas) using part of the same archival data as we used. However, we found that this maser feature is not the best to represent the annual parallax to S269 IRS 2w because the morphology is remarkably elongated in the east-west direction. For this study we have selected another maser feature showing simpler morphology.This makes the new annual parallax estimate more credible. Our newly obtained annual parallax is 0.247 ± 0.034 mas, corresponding to 4.05 +0.65 −0.49 kpc. This value is well consistent with the 3.7-3.8 kpc obtained using the kinematic distance estimates and photometric distance modulus. We considered two hypotheses for the water maser spatial distribution, a bipolar outflow and an expanding ring, in a kinematic model fitting analysis with a radially expanding flow. At this stage, any conclusions about the systemic proper motion could not be drawn from the kinematic analysis. Alternatively, we evaluated the mean proper motion to be (0.39 ± 0.92, −1.27 ± 0.90) mas yr −1 eastward and northward, respectively, from the obtained proper motions of the detected water maser features. The newly obtained annual parallax and mean proper motion give the peculiar motion of S269 IRS 2w to be (U s , V s , W s ) of (8 ± 6, −21 ± 17, 1 ± 18) km s −1 .

Aims. Cool, evolved stars have copious, enriched winds. Observations have so far not fully constrained models for the shaping and acceleration of these winds. We need to understand the dynamics better, from the pulsating stellar surface to ∼10 stellar radii, where radiation pressure on dust is fully effective. Asymmetric nebulae around some red supergiants imply the action of additional forces. Methods. We retrieved ALMA Science Verification data providing images of sub-mm line and continuum emission from VY CMa. This enables us to locate water masers with milli-arcsec accuracy and to resolve the dusty continuum. Results. The 658, 321, and 325 GHz masers lie in irregular, thick shells at increasing distances from the centre of expansion. For the first time this is confirmed as the stellar position, coinciding with a compact peak offset to the NW of the brightest continuum emission. The maser shells overlap but avoid each other on scales of up to 10 au. Their distribution is broadly consistent with excitation models but the conditions and kinematics are complicated by wind collisions, clumping, and asymmetries.