Call for Observations
AAVSO Alert Notice 809 announces an imminent campaign on the very young (and bright) accreting star AB Aur, in support of HST observations planned for 2023.
One set of HST observations has been completed, and the final set of HST observations will take place in February, but observers are asked to observe AB Aur beginning immediately and continuing through the end of the observing season. Building the light curve in the weeks leading up to the HST observations is essential so that, as the team say "we have a complete and accurate understanding of the star’s accretion activity and the behavior of its variability." Observers will be notified about the exact HST dates as soon as the information becomes available. Continuing: "Recently, a pointlike source has been detected with direct imaging of the circumstellar disk of AB Aur, indicating the potential existence of an accreting protoplanet at an orbital distance of ~93 au. However, unresolved features of protoplanetary disks can mimic planets by scattering light from the central star, causing false-positive signals — a major challenge in validating candidate protoplanets. Additional evidence is required to validate the existence of the protoplanet candidate, AB Aur b. Our team has an approved HST program that will confirm or refute the existence of the candidate protoplanet with accretion light echoes. We seek to answer the question: Is emission from this pointlike feature a bona fide accreting protoplanet, or is it an unresolved compact disk structure seen in scattered light? If flux from the companion source varies synchronously with the host star, that would point to the disk scattering scenario, whereas uncorrelated behavior would support the planet interpretation.
The nature of this experiment relies heavily on variability of the central star, and so it is essential that we understand the nature of its variability to the fullest extent during the months leading up to, and overlapping with, the HST observations. This monitoring campaign will provide critical support for the success of our HST program by enabling us to recover the characteristics of AB Aur’s variability. New science resulting from this campaign will be published in the Astrophysical Journal alongside the HST results as a multi-part series."
Therefore they request CCD observations, and for further (important) details on how to make these, use the link above. Observers have already begun work!
Studying the Sun's Birth Cluster
The Sun is thought to have been formed within a star cluster. Studies of an isotope of Aluminium indicate that a direct injection of these materials from a nearby core-collapse supernova should have occurred in the first 105 years of the solar system, and thereby within the duration of star formation in the Sun’s birth cluster. Here a Japanese study revisits the number of stars in the Sun’s birth cluster from the point of view of the probability for acquiring at least one core-collapse supernova within this time and environment, and finds that the number of stars in the birth cluster can be significantly larger than that previously considered, depending on the duration of star formation. |
Making the Solar SystemThis is the title of an article by John Chambers, where he models the early stages of planet formation in the Solar System, including continual planetesimal formation, and planetesimal and pebble accretion onto planetary embryos in an evolving disk driven by a disk wind.
The aim is to constrain aspects of planet formation that have large uncertainties by matching key characteristics of the Solar System, and the model produces a good fit to these characteristics for a narrow range of parameter space. Planetary growth beyond the ice line is dominated by pebble accretion whereas planetesimal accretion is more important inside the ice line. Pebble accretion inside the ice line is slowed by higher temperatures, partial removal of inflowing pebbles by planetesimal formation, pebble accretion further out in the disk, and increased radial velocities due to gas advection. The terrestrial planets are prevented from accreting much water ice because embryos beyond the ice line reach the pebble isolation mass before the ice line enters the terrestrial-planet region. When only pebble accretion is considered, embryos typically remain near their initial mass or grow to the pebble-isolation mass. Adding planetesimal accretion allows Mars-sized objects to form inside the ice line, and allows giant-planet cores to form over a wider region beyond the ice line.
(The term pebbles is used to refer to solid masses that are a 'step up' from planetesimal dust, and are typically a few mm to several cm in size). IM LupiNo, not a comment on my state of mind, but a well-studied nearby forming star with a visible dusty disc.
 A recent study looked at the proposition that observations of protoplanetary discs provide information on planet formation and the reasons for the diversity of planetary systems.
The key to understanding planet formation is the study of dust evolution from small grains to pebbles. Smaller grains are well-coupled to the gas dynamics, and their distribution is significantly extended above the disk midplane. Larger grains settle much faster and are efficiently formed only in the midplane. By combining near-infrared polarized light and millimeter observations, it is possible to constrain the spatial distribution of both the small and large grains. They aimed to construct detailed models of the size distribution and vertical/radial structure of the dust particles in protoplanetary discs based on observational data. In particular, they are interested in recovering the dust distribution in the IM Lup protoplanetary disk, shown above (the light from the central star has been suppressed from the image, courtesy the SPHERE instrument at ESO Chile). |
