Symposium 348 - Poster Abstracts


An upper limit on the energy density of the gravitational wave background and on variations of the gravitational potential measured with the pulsar timing.

Fedorova, Viktoriya

Timing of millisecond pulsars gives a possibility to establish an upper limit on the energy density of the gravitational wave background and on variations of the gravitational potential in the vicinity of the Solar System. Measurements are based on pulsar timing observations at Parkes observatory in 1995 — 2010. The fractional instability of the difference of the pulsar ensemble and the terrestrial time scales PTens−TT(BIPM2011) at the interval 15 yr σz = (0.6 ± 1.6)·10−15. This value corresponds to the upper limit of the energy density of the stochastic gravitational wave background Ωg h2 ∼10−10 and variations of the gravitational potential ∼ 10−15 at frequency 2 · 10−9 Hz.

Monitoring of optical magnitudes of quasars in line with the link ICRF - Gaia CRF

Damljanovic, Goran

We collected the optical magnitudes, mostly V and R, of 47 QSOs during two and half years (period mid-2013 - end of 2015) using ground-based telescopes. These QSOs were chosen for the link ICRF - future Gaia CRF. The instruments are: two TAROT telescopes, the Telescope Joan Oro (TJO, robotic one), and 6 telescopes in the region Serbia-Bulgaria-Austria. In Serbia, it is the 60 cm ASV one (Astronomical Station Vidojevica). The 60 cm (Belogradchik ) telescope, 2 m one (Rozhen Observatory), 50/70 cm Schmidt-camera (Rozhen) and 60 cm one (Rozhen) are in Bulgaria. The 1.5 m Leopold Figl instrument is in Austria. We wanted to investigate the variability of QSOs and to compare ground-based values with Gaia G-mag. To do that we use our V and R data and suitable transformation to get the G mag of observed QSOs. The light curves of some QSOs are presented here, but it is not possible to compare our values with the Gaia DR1 ones because until now there has been no corresponding epoch for each Gaia G magnitude. Only, there is the_x000D_ average G value. We hope that information will exist in the next Gaia realization.

Detection of Exoplanets in Multisystem Stars Using Quantization of Orbits

Morcos, Abd El Fady

Detection of the exoplanets in multisystem stars represents one of the important tasks in the coming interval of time. Thousands of multisystem in particular triple systems have been observed. The detection of the nature of the third body as a planet represents a hard question to be answered in triple systems. In a previous theoretical trial, Morcos in 2013, derived a simple relation, in the framework of scale relativity (Nottale (1997)), to find the orbital period of solar system plants by using a quantized form. That formula has been adapted to calculate the quantum orbital number of some exoplanets (Morcos, et al (2016)). In this work, the previously mentioned relation has been reformed using Hill radius of Margot (2015) to detect exoplanets in multisystem stars. The results may through a light on detection of the third body as an exoplanet by using the quantization of the body's orbit.

Discovery of two new hot Jupiters: WASP-163 b and WASP-170 b

Barkaoui, Khalid

We present two new hot Jupiters, WASP-163 b and WASP-170 b, discovered by the WASP-South survey [Pollacco et al. 2006]. We performed a combined analysis of radial velocity data obtained with the CORALIE spectrograph mounted on the 1.2 m Euler-Swiss telescope [D. Queloz et al. 2001] and follow-up transit observations with the TRAPPIST-North [M. Gillon et al. 2017], TRAPPIST-South [M. Gillet et al. 2011; E. Jehin et al. 2011], NITES [McCormac et al. 2014] and Euler telescopes, to determinate the system parameters (K. Barkaoui et al. in prep). WASP-163 b and WASP-170 b are slightly larger than Jupiter while being about twice more massive, and are in short orbits (<3 days) around bright (V<13) solar-type stars. The radii of WASP-163b and WASP-170b are well reproduced by classical models of irradiated giant planets [J. J. Fortney et al. 2017]. This discovery made use of a new 60 cm robotic telescope, TRAPPIST-North, installed in spring 2016 at Oukaimeden Observatory in Morocco. It is an instrumental project led by the University of Liege (Belgium), in collaboration with the Cadi Ayyad University of Marrakech (Morocco), that is, like its southern twin TRAPPIST-South, totally dedicated to the observations of exoplanet transits and small bodies of the solar system.

Astrometric Data Reduction (JASMINE case)

Yamada, Yoshiyuki

Astrometric data reduction is very tough work with complex system identification. We Japanese team plan Nano-JASMINE and Small-JASMINE missions.  Observational strategyof Nano-JASMINE is very similar to that of Gaia, and data reduction software development is being done as collaboration with Gaia AGIS team.  On the other hand, Small-JASMINE will observe bulge region with step-stare strategy.  We are now start software develpment.  International Collaboration(s) will be also planned.Astrometric Data Reduction will be done by iterative least square fit, and need to very large matrix inversion.  Stellar motion of primary stars are simple, but calibration model will become complex. Matrix inversion part will be hard computational work but relatively simple as a software enginnering problem. But matrix generation part will need to be flexible because the systems model will change during the mission. It may be challenge in software development. We will discuss how the software development will be done in JASMINE case, and which point can be common with other astrometric missions like Theia. 

Mass Discrepancy-Acceleration Relation from Giant Elliptical Galaxies to Dwarf Galaxies

Tian, Yong

The discrepancy between the dynamical mass and the baryonic mass is strongly related to the gravitational acceleration of 153 spiral galaxies from SPARC database. This is called the mass discrepancy-acceleration relation (MDAR). We studied an extensive elliptical galaxies catalog of giant elliptical galaxies and dwarf galaxies (Dabringhausen & Fellhauer 2016). We found that the MDAR of 500 elliptical galaxies agreed well with the result in spiral galaxies (McGaugh et al. 2016).

Tycho-Gaia vs Gaia DR2

Michalik, Daniel

The second Gaia data release (Gaia DR2; April 2018) contains five parameter astrometry for more than one billion stars. The underlying model assumes all stars to exhibit single star behaviour, i.e. to follow a uniform linear proper motion trend._x000D_ For 2 million stars we can obtain long temporal baseline proper motions by combining Gaia DR2 data with Tycho-2 positions from 1991.25, similar to the Tycho-Gaia Astrometric Solution (TGAS) in Gaia DR1. We present a comparison of instantenous Gaia DR2 proper motions with DR2-based Tycho-Gaia long-term trends, and a goodness-of-fit measurement that describes the agreement between the datasets. The latter allows us the detection of candidates for stars hosting stellar or sub-stellar companions fainter than the Gaia detection limit.

Exoplanets detection using empirical mode decomposition

Vasconez, Christian

The ultimate goal of exoplanets exploration is to discover potential habitable planets and even finding evidence of life beyond [Mayor & Queloz, 1995; Gillon et al., 2017; Alberti et al., 2017]. In fact, together with the technology, astrometry continuously reaches new levels of accuracy and precision, getting us closer to these goals. Now, it becomes crucial to improve and search new methods for astrophysical-information extraction from astrometric data. Here, an adaptive and a posteriori decomposition method, in which the basis functions are directly derived from the non-stationary data, is applied. This method, the empirical mode decomposition (EMD) [Huang et al., 1998] is used to study the public photometric data from the Kepler space mission. We focus on the system Kepler-41, where we identified two clear timescale contributions, respect to less-energetic modes. The first of these modes is positively attributed to Kepler-41b [Santerne et al., 2011]. Meanwhile, the second mode of the system let us to propose the existence of a non-identified exoplanet, transiting its solar-type star with an orbital period of 4.71375 days, and a semimajor axis of 0.05654 AU.

Using mHz QPOs to put constraints on neutron star size and equation of state

Stiele, Holger

4U 1636-536 is a well-studied LMXB, consisting of a neutron star (NS) in a 3.8 hr orbit with a companion star of about 0.4 solar masses. Showing the full range of rapid time variability, 4U 1636–53 is an ideal source for studying nuclear burning on the surface of a NS._x000D_ We performed a variability study of archival XMM-Newton data of 4U 1636-536 and investigated the energy dependence of its low frequency variability. Here we present the results of our waveform analysis and phase resolved spectral investigations of the mHz quasi-periodic oscillations (QPOs). Our study showed that the oscillations are not caused by variations in the blackbody temperature of the NS, but revealed a correlation between the change of the count rate during the mHz QPO pulse and the spatial extent of a region emitting blackbody emission. The maximum size of the emission area allowed us to obtain a lower limit on the size of the NS that rules out equations of state that prefer small NS radii. Up-coming NICER data will allow us to reduce the statistical uncertainty in the lower limit on the NS radius, which together with better estimates of the hardening factor and distance, will allow for improved discrimination between different equations of state and compact star models.

Analysis of data modern astrometric catalogues in GAIA era.

Akhmetov, Volodymyr

The new big catalogues of proper motion were created using of GaiaDR1 data. The names of these catalogues are HSOY, UCAC5, GPS1 and PMA. Using three or more catalogues in Wielen method it is easy to estimate the external accuracy of each of them. The random errors of stellar proper motions had been calculated based on the common objects from HSOY, UCAC5, GPS1 and PMA catalogues. From a comparison of PMA data with same stars from the UCAC5, GPS1 and HSOY catalogues, the equatorial components of the mutual rotation vector of these coordinate systems were determined. The angular velocities of mutual rotation of the PMA and UCAC5, HSOY, GPS1 reference frames change within range from 0.2 to 2.0 mas yr-1. The estimation of systematic and random errors of the stellar proper motions of the PMA, HSOY and GPS1 catalogues in the faintest magnitude range had been done via an analysis of formal proper motions of extragalactic objects are containing in these catalogues. Also, comparisons of stellar proper motions of these catalogues with Gaia DR2 data was planned to carry out, when it will be released.

Geodetic VLBI, Earth rotation and the Sagnac effect

Titov, Oleg

Geodetic Very Long Baseline Interferometry (VLBI) measures the group delay and phase delay rate in the barycentric reference frame. These both observables are sensitive to the geocentric velocities of the telescopes. This results in a non-zero closure delay and closure delay rate (as a sum of the three values around the closed triangle of baselines). The group delay equation includes a term consistent to the Sagnac effect (usually applied to the ring laser interferometer technique or GNSS modeling) and, therefore, could be used to estimate the instantaneous vector of the Earth angular velocity. However, the delay rate suggests more effective way to do this job because it manifests as the Sagnac effect in the primary term of the relativistic model. The instantaneous vector of the Earth angular velocity is estimated with accuracy of  10-12 - 10-13 1/sec with a small set of modern geodetic VLBI data. This provides an opportunity to detect the Thomas (geodetic) precession, the Lense-Thirring effect (frame-dragging) and even the angular rotation of the Galaxy using the full 40-year set of geodetic VLBI observations.

Mixture Model for Kinematics and Memberships of Open Cluster

Shao, Zhengyi

The Mixture-model approach is improved to measure the kinematics of open clusters, while all astrometric data, such as the coordinate position, proper motion and radial velocity, are used simultaneously to separate the motion of the cluster from that of the field stars. A Bayesian inference approach is employed to deal with the case of missing data of proper motion or radial velocity, and the Bayesian evidence is calculated to estimate the necessity of the mixture-model,since it is a quantitative identification of the existence of a cluster. The involving of multiple kinds of observational data, especially the high-precision radial velocity, significantly decreases the contamination degree of the cluster and field stars, and leads to the much more accurate value of the mean proper motion of the cluster. Based on the UCAC5 and radial velocities from RAVE and APOGEE, about 2000 clusters are determined. Meanwhile, the kinematic membership probabilities of individual stars are calculated. This method is expected to apply to the homogenous data from GAIA-DR2 to establish the cluster sample with full kinematic parameters. Furthermore, the dynamics of the Milky way disk will be analyzed by tracing of the open clusters. 

Machine Learning for RR Lyrae Stars

Zhang, Yanxia

We explore machine learning to target RR Lyrae stars from large survey databases (SDSS and GALEX). Classification of RR Lyrae stars from other types of stars belongs to the imbalance learming issue. Therefore the usual machine learing algrithms are not fit for this kind of issue. In this paper,cost-sensitive support vector machine,cost-sensitive random forest and fast boxes are applied to select RR Lyrae stars from other types of stars. Experimental results show that fast boxes is the best performer and the infomation added from ultraviolet band is helpful to seperate RR Lyrae stars.

Observing in the past thanks to the Gaia astrometric reference star catalogue

Arlot, Jean-Eudes

The arrival of the Gaia astrometric reference star catalogue is not only a giant step in the astrometric accuracy allowing to measure new unknown small motions of solar system objects but also to observe in the past with today accuracy. In fact, accurate astrometry is performed since about one century after the use of photographic plates. The measures made at the time of the old observations used old reference catalogues, the accuracy of which being between 500 mas and one arcsec. We will show how we are making new measures and new reductions of photographic plates thanks to the Gaia reference catalogue allowing to provide valuable data and pre-discoveries of recently observed objects.

Gaia DR1 Evidence of Disrupting the Perseus Arm

Baba, Junichi

We have discovered a clear sign of the disruption phase of the Perseus arm in the Milky Way using Cepheid variables, taking advantage of the accurately measured distances of Cepheids and the proper motions from Gaia Data Release 1. Both the Galactocentric radial and rotation velocities of 77 Cepheids within 1.5 kpc of the Perseus arm are correlated with their distances from the locus of the Perseus arm, as the trailing side is rotating faster and moving inward compared to the leading side. We also found a negative vertex deviation for the Cepheids on the trailing side, -27°.6, in contrast to the positive vertex deviation in the solar neighborhood. This is, to our knowledge, the first direct evidence that the vertex deviation around the Perseus arm is affected by the spiral arm. We compared these observational trends with our N-body/hydrodynamics simulations based on a static density- wave spiral scenario and with those based on a transient dynamic spiral scenario. Although our comparisons are limited to qualitative trends, they strongly favor the conclusion that the Perseus arm is in the disruption phase of a transient arm. 

The effects of the Galactic structures on Solar motion measurements

Kashiwada, Yuki

Measuring the Solar motion is a long-standing problem in Galactic astronomy. Although most previous studies were based on the axisymmetric kinematic models to measure the Solar motion, it is known that the non-axisymmetric Galactic structures (i.e. a bar and spiral arms) affect the kinematics of nearby stars. In this study, we therefore investigated the effects of the bar and spiral arms on the Solar motion measurement using the 'mock' Gaia DR2 data for the purpose of determining the solar motion with Gaia. The mock data are generated from 3D N-body/hydrodynamic simulations of a bar potential, rigidly rotating spiral potential (i.e., density wave), and dynamically evolving barred spiral models (Baba 2015; Baba et al. 2018). Applying the Oort-Lindblad and Ogrodonikov-Mile models to the mock data, we evaluated the effects of the spatial distributions and velocity structures (e.g. velocity ellipsoids and substructures) of sample stars. Using Bayesian analysis, we found that the difference between velocity dispersions of sample stars does not have a large influence on the values of the Solar motion in the Oort-Lindblad model. We will also discuss the effects of tilts of velocity ellipsoids, resonance orbits, selections of sample stars.

Strong gravitational lensing by elliptical and spiral galaxies in modified Newtonian dynamics

Ko, Chung-Ming

Modified Newtonian dynamics (MOND) is a viable alternative to dark matter halo in interpreting the missing mass problem in galaxies. Even if MOND were not a fundamental theory, practically it is an effective way to estimate the baryonic mass of galaxies. We study strong gravitational lensing of galaxies in the framework of MOND. To work out the lensing mass in MOND, we adopt Herquist-like model for ellipticals and Kuzmin-like model for spirals. We compare the lensing mass with baryonic mass deduced from other methods.

The automated morphological classification of galaxies from the SDSS at z<1.0 by the machine learning technique

Vavilova, Iryna

We evaluated a new approach for the automated morphological classification of big samples of galaxies which is based on the combination of three methods: visual classification for training samples; diagrams «color indices – concentration index»; machine learning technique (Random forest).  This approach was tested and applied for the SDSS samples of 317,018 galaxies at z<0.1 (Dobrycheva, Vavilova, Melnyk, Elyiv, 2017, arXiv:1712.08955).  Namely, we used a well-known fact that galaxy morphological type is correlated with the color indices, luminosity, de Vaucouleurs radius, inverse concentration index etc. We plotted the diagrams of color indices g-i and one of these parameters and discovered that these parameters may be used for galaxy classification into three classes: E -- elliptical and lenticular, S -- types Sa-Scd, and L -- types Sd-Sdm and irregulars. The accuracy is 98% for E, 88% for S, and 57% for L types. The combinations of "color indices g-i and inverse concentration index R50/R90' and "color indices g-i and absolute magnitude M_r" gave the best result:  143263 E type, 112 578 S type, 61177 L type (Dobrycheva, Melnyk, Vavilova, Elyiv, 2015, Astrophysics).  After this, we undergone a training sample of 5,000 galaxies classified visually into early E (E, S0, S0a) and late L (Sa to Irr) types using a machine learning technique. To define an accuracy of classifiers we applied the 5-folds validation and found that Random Forest provides the highest accuracy. Applying it to the SDSS DR9 sample of 60,561 galaxies at z<0.1 we obtained that 47% E and 53% L types are among these galaxies.To be sure in this approach, we prepared a sample of about 1,800,000 galaxies at z<1.0 and provided the automated morphological classification. The effectiveness of this approach for galaxies at different cosmological scales, details of creation of this sample and accuracy of applied methods, as well as the obtained results will be discussed in this report. 

Analysis of the parameters of the DM Halo around the non-radially oscillating disk

Mirtadjieva, Karamat

We study the dependence of the evolution of a nonlinearly nonradially disk oscillating in its plane, depending on the basic parameters of the DM Halo. The DM Halo stabilizes the instabilities in the plane of the disk, but destabilizes its vertical oscillations. The global disk structure is dependent strongly on the mass and shape of the DM Halo. The evolutionary dependences of the oscillation process versus the indicated parameters of the DM Halo are constructed.

Microlensing and time delays in gravitational lensed quasars

Akhunov, Talat

Gravitational lensing offers a unique tool to study the mass distribution of the lens, the structure of the light source as well as the physics of the Universe. However, any signi?cant contribution to these endeavours requires some continuous and detailed investigations of each known gravitational lens system. Therefore, we conducted optical monitoring of the gravitationally lensed systems H1413 + 117, B1422 + 237, PG1115 + 080, SBS1520 + 530, FBQ0951 + 2635 at the Maidanak Observatory in Uzbekistan for a long time. Thus, we obtained long-term series of observations, the photometric analysis of which gave us the following results.H1413+117: we analysed the V- and R-band light curves and V–R colour variations of the A–D components which show short- and long-term brightness variations correlated with colour variations. We have derived the new values of the time delays: ?tAB =-17.4 ± 2.1, ?tAC =-18.9 ± 2.8 and ?tAD = 28.8 ± 0.7 days (B and C are leading, D is trailing). We propose to characterize two kinds of micro-lensing events: micro-lensing for the A, B, C components corresponds to typical variations of ~10-4 mag/d during all the seasons, while the D component shows an unusually strong micro-lensing effect with variations of up to ~10-3 mag/d during 2004 and 2005.PG 1115+08: we found new values of the time delays in this GLS: ?tBA = 4.4±3.2, ?tAC = 12.0±2.5 and ?tBC = 16.4±3.5 days and that A1+A2 lensed components of the system might have undergone microlensing.B1422+237: we were able to get light curves for A,B and C lensed components which show us both activity of the source-quasar and presence of microlensing.FBQ0951+2635, SBS1512+530: we obtained light curves that show small-amplitude intrinsic variations of the quasar on time scales of about 100 days (in SBS1520+530). Variable magnitude di?erence between the images of the quasars shows the presence of microlensing variations in these systems.

New catalogue of extragalactic objects in the GAIA era

Khramtsov, Vladislav

In the GAIA era it is a crucial task of separation extragalactic objects from the galactic ones to test reference frame. We solved this problem with classification of objects due to optical-infrared colour information and created a new photometric catalogue of about 10 millions extragalactic objects from ALLWISE, Pan-STARRS DR1 and NOAO Source Catalogue (NSC) cross-identification. To create this catalogue, we employ Sparse Autoencoders (SAs) – machine learning technique for automatic feature extraction. We show that SAs provide precise star-galaxy separation in optical-infrared range without using any prior knowledge about types of objects. Separation were done using supervised classification in the high-dimensional sparse colour space by Support Vector Machine method.For investigation of separation accuracy, we tested catalogue of extragalactic sources using absolute proper motions from PMA catalogue; for this we cross-matched our resulting catalogue objects with PMA catalogue objects. We found that mean formal proper motion of these objects equals zero. Also we employ kinematic analysis: we investigated components of rotation tensor of our system according to solid-body rotation model; in result, all rotation components in faint part of magnitudes are zeros confirming that our objects are distant ones. Result was compared with same tests for other catalogues of extragalactic sources: ALLWISEAGN, Milliquas and WISExSCOS_photoz.In near future, we plan to test GAIA DR2 proper motions with our own catalogue.

State-of-the-art Hubble Space Telescope PROper MOtion (HSTPROMO) catalog of Galactic globular clusters. New insights and results.

Libralato, Mattia

With the advent of Gaia, astrometry is experiencing a new Renaissance. Although the Gaia mission will make important breakthroughs in different scientific topics, stars in crowded fields and at the faint end of the color-magnitude diagrams are and will be out of Gaia's reach, leaving again Hubble Space Telescope (HST) observations the unique way to obtain high-precision astrometric measurements for these stars.I present the continuation of the HST-based proper-motion analysis of Galactic globular clusters started in 2014, characterized by significant improvements in many aspects of the data reduction. As a benchmark of the state-of-the-art astrometry and photometry achieved with the HST data, I performed an all-around analysis of the globular cluster NGC 362. I studied the cluster’s internal kinematics and that of its multiple stellar populations. Furthermore, I investigated whether this cluster rotates in the plane of the sky and its absolute proper motion.

Unsupervised photometric galaxy clustering: Analysis of Euclid and DES bands with UPMASK

Carvalho, Ana

Galaxy Clusters are essential objects to study galaxy evolution as well as the dark sector of the universe. However, one of the biggest challenges of this study is to know which galaxies belong to the cluster and which galaxies are field galaxies, using the less possible ammount of a priori information on what a cluster is and not knowing the precision and accuracy of the individual distance of each galaxy. UPMASK, or Unsupervised Photometric Membership Assignment in Stellar Clusters, is a method created to study star clusters, when the distance is not known or poorly determined. This method uses heuristics and statistical analysis to separate a cluster from the field, without any basis on theoretical models, and consequently without strong a priori statements, of what a cluster is made of. It operates with minimal information from astrometry and photometry. In this poster we will show the results of a modified version of UPMASK optimized to study galaxy clusters. We present our findings about the potential of applying the UPMASK to the study of galaxy clusters without prior knowledge about their galaxy redshift or model distributions. We test the method using simulations that include the luminosity bands of DES and the forthcoming ESA/Euclid space mission.

Omega Centauri: HST internal kinematics

Bellini, Andrea

We look at the internal kinematics of the multiple stellar populations of the globular cluster ? Centauri in an external Hubble Space Telescope (HST) field located at about 3.5 half-light radii from the center of the cluster. Thanks to the over 15-yr long baseline and the exquisite astrometric precision of the HST cameras, well-measured stars in our proper-motion catalog have errors as low as ~10 µas yr-1, and the catalog itself extends to near the hydrogen-burning limit of the cluster. We show that second-generation (2G) stars are significantly more radially anisotropic than first-generation (1G) stars. The latter are instead consistent with an isotropic velocity distribution. In addition, 1G stars have excess systemic rotation in the plane of the sky with respect to 2G stars. We show that the six populations below the main-sequence (MS) knee identified are associated with the five main population groups recently isolated on the upper MS in the core of cluster. Furthermore, we find both 1G and 2G stars in the field to be far from being in energy equipartition, with ? 1G=-0.007+/- 0.026 for the former and ? 2G=0.074+/- 0.029 for the latter, where ? is defined so that the velocity dispersion s µ scales with stellar mass as s µ proportional to m-? . The kinematical differences reported here can help constrain the formation mechanisms for the multiple stellar populations in ? Centauri and other globular clusters.

Galactic rotation curve beyond the solar circle out to R0+10 kpc

Dambis, Andrey

We use the sim 12000 O-A-type star sample in the Galactic anticenter direction from the catalog of Monguio et al. (2013, 2014) with photometric distances (zero point calibrated via TGAS trigonometric parallaxes) and other parameters determined from Stroemgren photometry and proper motions from UCAC5 and GPS1 catalogs to analyze the run of the Galactic rotation curve and periodic variations of rotation velocity due to spiral density waves in the Galactocentric distance interval from R0 to R0+10 kpc. We find the smoothed rotation curve to be almost flat in the Galactocentric distance interval considered with a small depression of circular velocity at R0+3 kpc. When Gaia DR2 data becomes available, the analysis will be repeated including the trigonometric-parallax based recalibration of the photometric distance scale for the objects considered.

Finding needles in the haystack: a comparison of outlier detection methods

Martínez-Galarza, Rafael

Upcoming large observational surveys such as the Large Synoptic Survey Telescope (LSST) will produce millions of irregularly-sampled astronomical light curves. The enhanced sensitivity and time-sampling strategies of LSST will open a new window for several fields of astronomy, including precision cosmology, variable stars, as well as the discovery and characterization of new solar system objects. However, the large volume of the data that LSST will produce will require sophisticated algorithms for processing and interpreting these light curves. One important related question is how to find the most anomalous light curves, those that are perhaps not explained by current models. In this talk I will discuss state-of-the-art anomaly detection methods that use machine learning to find needles in the upcoming haystack of data. I will discuss several approaches to feature extraction for irregular light curves, including the use of auto-encoding recurrent neural networks, and the performance of several anomaly detection algorithms with respect to the features used. I will show the results of applying these methods to several time domain surveys, including SDSS's Stripe 82 and the All Sky Automated Survey (ASAS) catalog of variable stars, and present some of the weirdest light curves found.

The Photometric LSST Astronomical Time-Series Classification Challenge (PLAsTiCC)

Martínez-Galarza, Rafael

PLAsTiCC is a community-wide challenge to spur development of algorithms to classify astronomical transients expected to launch in the summer 2018. The Large Synoptic Survey Telescope (LSST) will discover tens of thousands of transient phenomena every single night. To deal with this massive onset of data, automated algorithms to classify and sort astronomical transients are crucial. PLAsTiCC, based on the highly successful Supernova Photometric Classification Challenge, will consist of a set of realistic LSST simulations of a variety of transient and variable phenomena. The challenge will be publicly available on a popular data science platform, encouraging algorithm submissions from outside the Astronomy community. I will present the major steps in getting this challenge ready, outline the several papers prepared that deal with the validation of the challenge data, and the metrics used to rank the participant's classiffiers and some early results of the communities response to it.

After 65 years dedicated to astrometric instrumentation, a Gaia successor is in sight

Høg, Erik

The astrometric foundation of astrophysics has been enormously improved by two ESA satellites that determined the positions, distances and motions of stars. I was fortunate to be at the right place and right time so that I could contribute towards various developments after beginning work as a student in 1953 at a new Danish meridian circle. These include the designs of:  a new method of astrometry by photon counting for the Hamburg meridian circle in 1960; a new design for the Hipparcos mission in 1975; the Tycho experiment for the Hipparcos satellite in 1981; direct-imaging on CCDs for the Gaia mission in 1992; and most recently, a Gaia successor in 2013 that should be launched in about twenty years. In April 2017 ESA approved our proposal (Hobbs et al. 2016, arXiv 1609.07325) to study a Gaia successor with infrared detecting capabilities. That proposal was one of three selected out of 26 submitted in response to ESA's call for new "Science Ideas" to be investigated for feasibility and technological developments. The study by ESA has resulted in the focal plane with NIR sensors shown on the poster at lower right.

Bayesian estimation and prediction of redshift-independent extragalactic distance errors

Chaparro, Germán

We present a methodology for estimating and predicting extragalactic distance errors in multi-measurement catalogs. Our estimation of errors is based on using well performing robust measures of the variance of the posterior distribution of extragalactic distance for individual galaxies. We apply those measures to the bootstrap sampled distribution that emerges when considering many distance estimations for individual galaxies with different distance determination methods. We create error data tables for galaxies in the Cosmiflows-3, HyperLEDA, and NED-D redshift-independent distance catalogs. Additionally, we are able to learn the systematics of the errors for distance determination with the TF relation and use this to create a Bayesian predictive model validated using a Bayesian p-value based on the Freeman-Tukey discrepancy measure. We use this model to predict missing/non-reported distance errors from the NED-D and HyperLEDA catalogs. Errors estimated or predicted in this work should be used in catalog-wide precision cosmology studies that require a full consideration of the true uncertainty of redshift-independent extragalactic distance determination.

The warped potential of the Milky Way revealed by Gaia DR2

Poggio, Eloisa

Among the open questions about Galaxy evolution, the origin and the dynamical nature of the Galactic warp is one of the most challenging. Possible candidates for generating warped discs are the triaxiality of dark matter haloes, a misaligned infall of gas and tidal interactions with satellite galaxies (among the others), but which one is at work in our own Galaxy is still unkown. The study of stellar kinematics could shed some light on this highly debated topic, given the intrinsic connection with the underlying forces. With the advent of the second Gaia data release, kinematics can be explored with exquisite precision on unprecedented spatial scales. We detect the large scale signature of the Galactic warp (up to distances of 7 kpc from the Sun) in the kinematics of two stellar samples having different typical age. The two samples contain respectively upper main sequence stars and giants, selected using 2MASS photometry and Gaia DR2 astrometry, without using individual extinction estimates. The signal shown by the two samples is similar, indicating that the mechanism producing the warp must be common to both dynamically young and old stellar populations. We conclude that the warp is a purely gravitational phenomenon, reflecting a warp in the gravitational potential of the Milky Way.

Dynamical Effects of Detected Giant Planets on the Habitable Zone in Binary Star Systems

Bazso, Akos

We present a survey of binary star systems with detected circumstellar extrasolar planets. The sample includes stars with separations up to 500 au. The presence of a Jupiter-like giant planet gives rise to a variety of gravitational interactions. Such interactions include mean-motion resonances (MMR) as well as secular resonances (SR). Secular resonances often entail highly eccentric motion. We use a semi-analytical method to find the locations of SRs, which are basically determined by the orbital precession frequencies of the massive bodies. For the systems at hand we investigate three possible orbital configurations of the giant planet: it is located either (1) exterior to the habitable zone (HZ) like in the solar system, (2) interior to the HZ like in case of Hot Jupiters, or (3) right inside the HZ. From the perspective of additional habitable terrestrial planets the last configuration is unpleasant. For the first configuration we demonstrate that there is always an SR interior to the giant planet's orbit. Under certain circumstances – depending on the system's architecture – this SR might fall into the HZ and cause highly eccentric motion of terrestrial planets. If additional MMRs are active this could even lead to the ejection of the terrestrial planet from the system. The second configuration is more safe in terms of SR, but including general relativistic perturbations SRs are possible, too. Generally, giant planets exterior to the HZ are less favourable in binary star systems. The majority of planets in our sample belongs to the second configuration, though, so we predict a fair chance to observe additional terrestrial planets in the HZ.

A comparison of planetary embryos collision outcome in binary and single star systems : perfect merging versus a more realistic model.

Bancelin, David

By now, observations of exoplanets have found nearly 90 binary star systems hosting 125 planets. We expect these numbers to increase as 50 – 70 % of the main sequence stars in the solar neighbourhood are members of binary or multiple systems. The planetary motion in binary star systems depends strongly on both the parameters of the stellar system (i.e. stellar separation and eccentricity) and the architecture of the planetary system (i.e. number of planets and their orbital behaviour). In case a terrestrial planet moves in the so-called habitable zone (HZ) of its host star, the habitability of such a planet depends on further requirements among which the amount of liquid water on its surface is certainly a crucial factor.Models of planetary formation either in single or binary star systems favour a merging approach to estimate the outcome of collisions occurring between Moon-to-Mars-sized embryos during the early stage of planetary formation. As a consequence, the size and water content of the body resulting from a collision are systematically overestimated because of the assumption of perfect merging.In our study, we simulate collisions of same-sized embryos (either Moon or Mars size) initially placed in the region between 0.9 and 1.1 au which are perturbed by a giant planet of Jupiter mass and a secondary star. In these simulations, we derive statistics for the impact velocities and angles. Our results show that in comparison with a corresponding single star systems, the impact velocities are significantly higher in binary star systems in case the giant planet and the secondary star induce a secular resonance in the studied area.Combining our results with more realistic collisions simulations using a GPU 3D-SPH (Smooth-Particles Hydrodynamics) code, we find for both single and binary regimes, a significant loss of water and material especially at low impact velocities when the impact angle is less than 45°.

Astrometric radial velocities from Gaia DR2 astrometric data

Liao, Shilong

High accuray astrometric data such as Gaia DR2 allow us to determine the line of sight velocities. We use the maximum-likelihood formulation to estimate the space velocity in moving clusters with the Gaia DR2 high accuracy astrometric data only. And then we compare the results with the spectroscopy results. The astrometric radial velocities are obtained with a RMS of about 0.50 km/s for the center of the cluster.

Field Distortion Model Based on Fredholm Integral

Zhou, Jianfeng

Field distortions in imaging process can cause serious loss of accuracy. These distortions are normally caused by geometric errors of imaging devices, installation errors or environmental vibration. We propose the Fredholm Integral Model to describe an imaging process with distortion. A polynomial approximation is proposed to estimate the distortion kernel with sufficient accuracy to micro-pixel.

Using Gaia DR2 astrometric data to identify QSOs

Liao, Shilong

QSOs are essential objects for astrometry, especially in building the celestial reference frame. Besides, QSOs are perfect nature objects to detect parallax and proper bias in astrometry mission such as Gaia because QSOs present no significant parallax. The non-detectable proper motion is a basic characteristic of quasars; therefore, an astrometric selection criterion based on near-zero proper motion can increase the purity of quasars in the mid-infrared color selected sample, as the latter is inevitably contaminated by false detections. Here we try to use the Gaia DR2 astrometric data and combine with the WISE data to select the largest sample of QSO candinates. This will be very useful in Gaia mission and related scientific research.

A Predicted Astrometric Microlensing Event by a Nearby White Dwarf

Smart, Richard

We used the Tycho-Gaia Astrometric Solution catalogue, part of Gaia Data Release 1, to search for candidate astrometric microlensing events expected to occur within the remaining lifetime of the Gaia satellite. Our search yielded one promising candidate. We predict that the nearby DQ type white dwarf LAWD 37 (WD 1142-645) will lens a background star and will reach closest approach on November 11th 2019 (± 4 days) with impact parameter 380 ± 10 mas. This will produce an apparent maximum deviation of the source position of 2.8 ± 0.1 mas. In the most propitious circumstance, Gaia will be able to determine the mass of LAWD 37 to ~3%.  We discuss this event and other work we are carrying out in preparation for the Gaia mission.

3D kinematics of the Galactic thin disc stars from the Gaia DR2 and PMA data.

Velichko, Anna

Joint usage of proper motions and radial velocities provided by the Gaia mission allows to get a full view about stellar kinematics in the solar neighborhood.Using kinematic criterium thin disk stars were selected from the ~7.2 mln Gaia DR2 subsample containing radial velocities, resulting in ~5 mln (~70%) stellar subset. For these stars of mixed spectral composition kinematic parameters of the Ogorodnikov-Milne model (OMM) from the Gaia DR2 and PMA data depending on distance to the stellar sample from 100 to 1000 pc were derived. We carried out two solutions of the OMM equations by the least square method: joint (proroper motions plus radial velocities) and separate (using proprer motions only).As a result, we can make several conclusions. First, 3D and 2D calculations give us very close values of the kinematic parameters. Second, using relation between value of V component of the solar peculiar velocity relative to the centroid chosen and mean age of stars included to the corresponding stellar sample (Dehnen & Binney(1998), Gontcharov (2012)), we decided that the latter for our stellar subsample of thin disk stars is about 4.0 Gyrs. Third, value of the rotational velocity of the Galaxy at the solar distance (8.0 pc, Vallee (2017)) Vrot derived from the PMA data is systematically lower than one derived from the Gaia DR2 data by about 15 km/s.We trace the OMM parameters depending on distance to the stellar sample. Note that the  ?3 and M12+ do not have any notisable trends depending on distance. ?2 and ?1 are meaningful only for the nearest stars up to 300 and 500 ps respectively, then they become equal to zero within 3s. M23+,M22+,M13+ also gradually decreases to zero while  M11+, on the contrary, increases with distance.  M33+ is not meaningful almost in all cases.

Potentially habitable circumbinary worlds in the Solar neighbourhood

Shevchenko, Ivan

We analyze avalable databases on binary stars in the Solar neighbourhood, and for each binary we (1) calculate the radii of the inner and outer borders of the annular circumbinary habitable zone (CBHZ), if present, and (2) calculate the radius of the circumbinary zone of orbital chaos (the circumbinary chaotic zone, CCZ). Then we identify those binaries for which the CCZ borderline is inside the CBHZ (i.e., the CCZ radius is greater than the CBHZ inner radius but smaller than the CBHZ outer radius). As soon as the CCZ border is just the place where a pile-up of circumbinary planets (CBP) is expected (both on theoretical and observational grounds), the identified stars may host potentially habitable CBP; therefore, they represent promising targets for future observations.

Massive identification of resonant and chaotic exoplanetary systems

Shevchenko, Ivan

Data on the known exoplanetary systems are considered to extract subsets of (1) multiplanet exosystems (exosystems with more than one planet) and (2) exosystems of binary (and, generally, multiple) stars. Both subsets are analyzed on the subject of the presence of resonant and/or chaotic orbital behaviours. For this purpose, numerical integrations of planetary orbits (with known and most probable values of parameters and initial conditions) are accomplished on suitable time intervals. The resonant behaviour is revealed by means of analyzing the time behaviour of the resonant arguments of mean motion resonances up to prescribed orders. The chaotic behaviour is revealed by means of computation of the maximum Lyapunov exponents. Lists of nominally resonant and chaotic exosystems are constructed, and their statistical analysis is performed.

The Gaia Archive Visualisation Service

Moitinho, André

Gaia, with its astrometric data of unprecedented quality is widely considered a transformative endeavour in Astronomy. The huge data volume delivered in the Gaia data releases is also transforming the way data exploration is done.With almost 1.7 billion sources as of Data Release 2, the information content of the Gaia Archive is unimaginable. In this poster we present the Gaia Archive Visualisation Service (GAVS). GAVS is both a platform for interactive visual exploration of the Gaia data; and a provider of intelligible visual representations of the enormous information content of the archive. Examples of these representations are the all sky density and flux maps which became the iconic images of the Gaia Data releases. Technical details are given, lessons learned and open challenges for Gaia and future missions are discussed.

On the evolution of the scale height of the Milky Way disc

Vitorino da Silva, André Filipe

In the absence of direct detections of dark matter, the study of dark matter induced perturbations in the Galactic disk is done by analysing the morphology and kinematics of the detectable constituents. These include the continuous interstellar medium, and discrete objects such as giant molecular clouds, individual stars and star clusters. One key morphological indicator is the scale height of the (thin) disc and its evolution. However, the scale height evolution of the different types of objects can be driven by different phenomena. These must be well understood if the  effects of dark matter perturbations are to be isolated.The scale height of open star clusters in the Milky Way exhibits a well known increase with age. This increase is usually attributed, in a vague way, to disc heating mechanisms similar to those that act on individual stars.  In this poster, we address the evolution of the scale height of open clusters from a different angle. We present a dynamical model that follows the orbits of open clusters and includes their disruption due to interactions with the disc, mostly encounters with giant molecular clouds. We show how simulations with this model reproduce the observed open cluster vertical distributions remarkably well. Still, the current compilations of open cluster parameters are affected by a number of selection effects and some of them are contaminated by significant numbers of non existing clusters. We discuss these sample effects in the light of the possibilities brought by Gaia Data Release 2 as well as future releases from Gaia and other astrometric surveys.

WFIRST Microlensing Exoplanet Characterization with HST Follow up Astrometry


More than 50 planets are discovered with the different ground based telescopes available for microlensing. But the analysis of ground based data fails to provide a complete solution. To fulfill that gap, space based telescopes, like Hubble space telescope and Spitzer are used. My research work focuses on extracting the planet mass, host star mass, their separation and their distance in physical units from HST Follow-up observations. I will present the challenges faced in developing this method.This is the primary mass measurement method to be used for NASA's top priority project (according to 2010 decadal survey) Wide Field InfraRed Survey Telescope (WFIRST) Exoplanet microlensing space observatory, to be launched in 2025. The unique ability of microlensing is that with WFIRST it can detect sub-earth- mass planets beyond the reach of Kepler at separation 1 AU to infinity. This will provide us the necessary statistics to study the formation and evolution of planetary systems. This will also provide us with necessary initial conditions to model the formation of planets and the habitable zones around M dwarf stars. 

XXX IAU General Assembly | ACV - Austria Center Vienna  | Bruno-Kreisky-Platz 1  | 1220 Vienna