Abstracts of the Monday Pitch Session

About proper motion of lensed QSOs in Gaia DR2

by Alex Bombrun, Maggie Lieu, Ivan Valtchanov, et al.

Even if not designed for cosmological studies; Gaia has been identified as a major source for the discovery of QSOs and lensed QSOs. Gaia not only provides new objects but also new information on these objects. Here we will focus on the proper motions of known lensed QSOs as derived in DR2. Whereas the proper motions of QSOs are statistically zero; the proper motions of lensed QSOs are significantly nonzero. However the information provided in DR2 is not sufficient to decide if these are true proper motions or artefact of the DPAC data processing.

Searching for multiple stellar populations in the GD1 stellar stream with Gaia

by Eduardo Balbinot, Ivan Cabrera-Ziri

Cold stellar streams are the remnants of globular clusters (GCs), objects which are known to have multiple stellar populations (MSP), i.e. a spread in light elements abundances and often Helium. Here, we look into the stellar stream GD1, a remnant of a GC, with an initial mass lower than any GCs known to have MSP. With the aid of Gaia, SDSS, and a variety of spectroscopic surveys we investigate the presence of MSP. We show that GD1 has the potential to be the lowest mass system at which this phenomenon is present, posing a new challenge to models of GC formation.

Shedding light on the Milky Way rotation curve with Gaia DR2

by Mariateresa Crosta, Marco Giammaria, Mario Lattanzi, et al.

We present the first attempt to apply the relativistic kinematics delivered by Gaia to trace the MW rotation curves within a general relativistic scenario. In particular; we have tested an axially symmetric; stationary and asymptotically flat Galaxy-scale metric. The mass inside a large portion of the Galaxy; far away from the central bulk; has been simplified as a pressure-less perfect fluid avoiding the bulge where resides the axis of symmetry. The study of the rotation curve profile of our Galaxy required the selection of the most suitable stellar tracers of the bulk circular velocity around the galactic center.

We selected DR2 sources according to the requirements for a proper 6-dimensional reconstruction of the phase-space location occupied by each individual star as derived by the same observer. The relativistic fit to the MW rotational data has been compared with well-studied classical models for the MW (MWC); which is comprised of a bulge; a stellar disk and a Navarro-Frenk-White (NFW) dark matter (DM) halo. To quantitatively asses this; a Monte Carlo Markov Chain (MCMC) analysis has been done and compared the results for the two models.

For the likelihood analysis the relativistic and MWC models appear almost identically consistent with the data. Nevertheless; as for the local baryonic matter density; estimated via the 00-term of then Einstein field equation; we have obtained a value that is perfectly in line with current estimates; which implies no need of extra-mass.

Discovery of a new nearby moving group

by Verena Fürnkranz, Joao Alves, Stefan Meingast

Today; we know that young groups of stars with similar age and kinematics can appear not only as clusters but also as extended groups; spanning several degrees across the sky. The wealth of data provided by the second data release of the Gaia mission delivers many new insights into such groups; particularly for their kinematics. Previous work suggested that the Pleiades cluster together with the AB Doradus moving group have a common origin.

In this talk; I will present further evidence of the common origin of the Pleiades cluster and the AB Dor moving group. Moreover; based on kinematic data available in Gaia DR2; I will also present proof for the existence of a previously unknown co-moving stellar group. In particular; I will speculate on the connection between this new group and already known clusters and associations; investigating a common origin scenario; similar to the Pleiades and the AB Doradus moving group.

Classical pulsators in the Magellanic Bridge as seen by OGLE and Gaia

by Anna Jacyszyn-Dobrzeniecka

The Magellanic Bridge; a direct evidence of LMC and SMC interactions; constitutes one of our closest tidally stripped stellar populations. I will present results of a three-dimensional study of classical and anomalous Cepheids as well as RR Lyrae stars in the area between the Magellanic Clouds. Classical Cepheids form a bridge-like connection that closely follows the neutral hydrogen and young population on-sky distributions. Anomalous Cepheids are more spread in every dimension; whereas RR Lyrae stars seem to resemble two overlapping extended structures rather than a bridge-like connection.

The analysis is mainly based on data from the OGLE survey that monitors the Bridge since 2010. I will also show the Gaia DR2 classical pulsators distribution that is consistent with our main results; especially in terms of older population. Moreover; I will also present a reanalysis of Belokurov et al. (2017) RR Lyrae candidates in the Bridge using Gaia DR1. Following their technique; we tried to reproduce their results of a bridge-like connection formed by old pulsators. I will show that we are not able to obtain similar results without many spurious sources located in the area of interest.

Stellar Stream map of the Milky Way Halo : Application of STREAMFINDER onto ESA/Gaia DR2

by Khyati Malhan

A panoramic map of the stellar streams of the Milky Way would be presented that was obtained based upon astrometric and photometric measurements from the Gaia DR2 catalogue. This was achieved using the STREAMFINDER algorithm to detect structures along plausible orbits that are consistent with the Gaia proper motion measurements. A rich network of criss-crossing streams in the halo was found. Some of these structures were previously-known; but several others were new discoveries. With these initial discoveries; we are starting to unravel the complex formation of the halo of our Galaxy.

The bulge and bar region seen by APOGEE and Gaia DR2

by Anna Queiroz, Cristina Chiappini, Friedrich Anders, et al.

We present a first analysis of the inner region of our Galaxy, using distances and extinctions derived by StarHorse (Queiroz et al 2018) Bayesian tool. Well constrained distances and extinctions were estimated using the latest releases of Gaia and APOGEE surveys, which provide astrometry, photometry, spectral atmospheric parameters and chemical abundances with high-resolution. Using a Bayesian approach is the only solution to get reliable distances in the Bulge region.

Indeed, with our method we can extend the volume for which reliable distances and extinctions can be derived with respect to those using only the Gaia parallaxes. With StarHorse we obtain typical distance uncertainties of 20% in this region. The method has been extensively tested with simulations and external samples, and it has been used by a wide range of publications studying the Milky Way.

We made a geometric selection of the bar and bulge region using StarHorse resulting distances from Gaia, 2MASS, WISE and PanSTARRS photometry for around 300 million stars without spectroscopy (Anders et al. in prep). We then focus our analysis on a sub-sample for which APOGEE information is also available, making an analysis of the kinematics and chemical properties of selected stars in the Bulge that trace the bar structure.

Rotating globular clusters in the Gaia era

by Alice Zocchi, Anna Lisa Varri

Globular clusters have long been considered to be spherically symmetric; isotropic; non-rotating stellar systems. However; this simple picture has been revolutionized by a series of recent discoveries about their kinematic and structural properties; which challenge our theoretical understanding of their formation and evolution. As a first step to address and describe the dynamical complexity of these systems; the family of LIMEPY models has been introduced (Gieles & Zocchi 2015). LIMEPY models are self-consistent; spherical; and non-rotating; with parameterised prescriptions for the energy truncation and for the amount of radially biased pressure anisotropy. However; for many GCs; rotation is important and cannot be neglected when describing their dynamics.

By including an angular momentum dependent term in the distribution function of LIMEPY models; we have developed a family of rotating models which will contribute to form a more realistic dynamical paradigm for this class of stellar systems (Zocchi & Varri; in prep.). I will present this new family of rotating models and their properties; and I will show an example of their application to describe the dynamics of globular clusters as probed by Gaia data.