Klemen Čotar
A5034131266- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Astro and Planetary Science
- Astrophysical Phenomena and Observations
- Remote Sensing in Agriculture
- Satellite Image Processing and Photogrammetry
- Geochemistry and Geologic Mapping
- Maritime and Coastal Archaeology
- Spectroscopy and Laser Applications
- Spectroscopy and Chemometric Analyses
- Remote Sensing and LiDAR Applications
- Historical Geography and Cartography
- Atmospheric Ozone and Climate
- Automated Road and Building Extraction
- Medical Imaging and Analysis
- Calibration and Measurement Techniques
- Forest Management and Policy
- Regional Development and Management Studies
- Geological Modeling and Analysis
- Molecular Spectroscopy and Structure
- Inorganic Fluorides and Related Compounds
- Scientific Research and Discoveries
University of Ljubljana
2018-2023
Slovenian Centre of Excellence for Space Sciences and Technologies
2015-2016
The ensemble of chemical element abundance measurements for stars, along with precision distances and orbit properties, provides high-dimensional data to study the evolution Milky Way. With this third release Galactic Archaeology HERMES (GALAH) survey, we publish 678 423 spectra 588 571 mostly nearby stars (81.2% are within <2 kpc), observed spectrograph at Anglo-Australian Telescope. This (hereafter GALAH+ DR3) includes all observations from GALAH Phase 1 (bright, main, faint 70%),...
The Galactic Archaeology with HERMES (GALAH) survey is a large-scale stellar spectroscopic of the Milky Way and designed to deliver chemical information complementary large number stars covered by $Gaia$ mission. We present GALAH second public data release (GALAH DR2) containing 342,682 stars. For these stars, collaboration provides parameters abundances for up 23 elements community. Here we target selection, observation, reduction detailed explanation how spectra were analysed estimate...
Open clusters are unique tracers of the history our own Galaxy's disk. According to membership analysis based on \textit{Gaia} astrometry, out 226 potential falling in footprint GALAH or APOGEE, we find that 205 have secure members were observed by at least one survey. Furthermore, 134 high-quality spectroscopic data use determine their chemical composition. We leverage this information study distribution throughout Galactic disk 21 elements, from C Eu. The radial metallicity gradient...
Massive sets of stellar spectroscopic observations are rapidly becoming available and these can be used to determine the chemical composition evolution Galaxy with unprecedented precision. One major challenges in this endeavour involves constructing realistic models spectra which reliably abundances. At present, large surveys commonly use simplified that assume atmospheres approximately local thermodynamic equilibrium (LTE). To test ultimately relax assumption, we have performed non-LTE...
We explore the fundamental relations governing radial and vertical velocity dispersions of stars in Milky Way, from combined studies complementary surveys including GALAH, LAMOST, APOGEE, NASA $Kepler$ K2 missions, $Gaia$ DR2. find that different stellar samples, even though they target tracer populations employ a variety age estimation techniques, follow same set relations. provide clearest evidence to date that, addition well-known dependence on age, depend orbital angular momentum $L_z$,...
Asteroseismology is a promising tool to study Galactic structure and evolution because it can probe the ages of stars. Earlier attempts comparing seismic data from {\it Kepler} satellite with predictions Galaxy models found that predicted more low-mass stars compared observed distribution masses. It was unclear if mismatch due inaccuracies in models, or unknown aspects selection function Using new K2 mission, which has well-defined function, we find an old metal-poor thick disc, as used...
The overlap between the spectroscopic Galactic Archaeology with HERMES (GALAH) survey & $Gaia$ provides a high-dimensional chemodynamical space of unprecedented size. We present first analysis subset this overlap, 7066 dwarf, turn-off, sub-giant stars. [...] investigate correlations chemical compositions, ages, kinematics for sample. Stellar parameters elemental abundances are derived from GALAH spectra spectral synthesis code SME. report Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr,...
We investigate the properties of 1262 red giant stars with high photospheric abundances lithium observed by GALAH and \Ktwo-HERMES surveys, discuss them in context proposed mechanisms for enrichment re-depletion stars. confirm that Li-rich giants are rare, making up only 1.2 per cent our star sample. use stellar parameters from third public data release survey a Bayesian isochrone analysis to divide sample into first-ascent branch clump stars, these classifications using asteroseismic \Ktwo....
Context. Binary stellar systems form a large fraction of the Galaxy’s stars. They are useful as laboratories for studying physical processes taking place within stars, and must be correctly taken into account when observations stars used to study structure evolution Galaxy. The advent large-scale spectroscopic photometric surveys allows us obtain samples binaries that permit characterising their populations. Aims. We aim sample double-lined (SB2s) by analysis spectra from GALAH survey in...
Previous studies have found that the elemental abundances of a star correlate directly with its age and metallicity. Using this knowledge, we derive ages for sample 250,000 stars taken from GALAH DR3 using only their overall metallicity chemical abundances. Stellar are estimated via machine learning algorithm $XGBoost$, main sequence turnoff precise as our input training set. We find stellar bulk accurate to 1-2 Gyr method. With these ages, replicate many recent results on age-kinematic...
Sparse open clusters can be found at high galactic latitudes where loosely populated are more easily detected against the lower stellar background. Because most star formation takes place in thin disc, observed population of far from Galactic plane is hard to explain. We combined spectral parameters GALAH survey with Gaia DR2 catalogue study dynamics and chemistry five old sparse high-latitude detail. find that four them (NGC 1252, NGC 6994, 7772, 7826) – originally classified 1888 not but...
GALAH is a large-scale magnitude-limited southern stellar spectroscopic survey. Its second data release (GALAH DR2) provides values of parameters and abundances 23 elements for 342,682 stars (Buder et al.). Here we add description the public radial velocities with typical accuracy 0.1 km/s 336,215 these stars, achievable due to large wavelength coverage, high resolving power good signal noise ratio observed spectra, but also because convective motions in atmosphere gravitational redshift...
Using data from the GALAH survey, we explore dependence of elemental abundances on stellar age and metallicity among Galactic disc stars. We find that abundance most elements can be predicted [Fe/H] with an intrinsic scatter about 0.03 dex. discuss possible causes for existence abundance-age-metallicity relations. a stochastic chemical enrichment scheme based size Supernovae remnants, show is expected to small, 0.05 dex or even smaller if there additional mixing in ISM. Elemental trends both...
ABSTRACT APOGEE and GALAH are two high resolution multi-object spectroscopic surveys that provide fundamental stellar parameters multiple elemental abundance estimates for about half a million stars in the Milky Way. Both observe different wavelength regimes use data reduction pipelines leading to significant offsets trends abundances common observed both surveys. Such systematic differences/offsets make it difficult effectively utilize them investigate Galactic spite of unique advantage...
Using GALAH survey data of nearby stars, we look at how structure in the planar (u,v) velocity distribution depends on metallicity and viewing direction within Galaxy. In with distance d < 1 kpc, Hercules stream is most strongly seen higher stars [Fe/H] > 0.2. The peak v value viewed galactic longitude, which interpret as due to gap between stellar more circular orbits being associated a specific angular momentum about 1640 km/s kpc. association particular supports bar resonant model...
In response to the increasing need for fast satellite image processing SPACE-SI developed STORM—a fully automatic chain that performs all steps from input optical images web-delivered map-ready products various sensors. This paper focuses on geometric corrections module and its adaptation very high resolution (VHR) multispectral images. ground control points (GCPs) extraction sub-module a two-step algorithm utilizes vector roads as reference layer delivers GCPs RapidEye with near pixel...
We use more than 872,000 mid-to-high resolution (R $\sim$ 20,000) spectra of stars from the GALAH survey to discern diffuse interstellar bands (DIBs). four windows with wavelength range 4718 4903, 5649 5873, 6481 6739, and 7590 7890 \AA, giving a total coverage 967 \AA. produce $\sim$400,000 medium (ISM) absorption features correct them for radial velocities DIB clouds. Ultimately, we combine 33,115 best ISM into six reddening bins $0.1 \,\mathrm{mag} < E\mathrm{(B-V)} 0.7\, \mathrm{mag}$. A...
We present isochrone ages and initial bulk metallicities ($\rm [Fe/H]_{bulk}$, by accounting for diffusion) of 163,722 stars from the GALAH Data Release 2, mainly composed main sequence turn-off subgiants 7000 K>T_{eff}>4000 K$ $\rm log g>3$ dex). The local age-metallicity relationship (AMR) is nearly flat but with significant scatter at all ages; even higher when considering observed surface abundances. After correcting selection effects, AMR appear to have intrinsic structures indicative...
We have identified a first group of 33 new candidates for symbiotic stars (SySt) the accreting-only variety among 600,255 so far observed by GALAH high-resolution spectroscopic survey Southern Hemisphere, more than doubling number those previously known. aims to high latitudes and this offers possibility sound Galaxy SySt away from usual Plane Bulge hunting regions. In paper we focus on M spectral type, showing an Halpha emission with peak in excess 0.5 above adjacent continuum level, not...
We present a study using the second data release of GALAH survey stellar parameters and elemental abundances 15 pairs stars identified by Oh et al. They these as potentially co-moving proper motions parallaxes from Gaia DR1. find that 11 very wide (>1 pc) do in fact have similar Galactic orbits, while further four claimed are not truly co-orbiting. Eight co-orbiting reliable abundances, we three those quite their abundance patterns, five significant [Fe/H] differences. For latter, this...
Using kinematics from Gaia and the large elemental abundance space of second data release GALAH survey, we identify two new members Fimbulthul stellar stream, chemically tag them to massive, multi-metallic globular cluster $\omega$ Centauri. Recent analysis had revealed stream in halo Milky Way. It been proposed that is associated with Centauri, but this proposition relied exclusively upon metallicities stars make association. In work, find our be metal-poor are enhanced sodium aluminium,...
Due to its proximity, the Orion star forming region is often used as a proxy study processes related formation and observe young stars in environment they were born in. With release of Gaia DR2, distance measurements complex are now good enough that three dimensional structure can be explored. Here we test hypothesis that, due non-trivial dynamics, age spread complex, chemical enrichment youngest by early core-collapse supernovae observed. We obtained spectra 794 with HERMES spectrograph at...
ABSTRACT The European Space Agency (ESA) Gaia mission has enabled the remarkable discovery that a large fraction of stars near solar neighbourhood are debris from single in-falling system, so-called Gaia-Sausage-Enceladus (GSE). This provides astronomers for first time with cohort easily observable, unevolved formed in extragalactic environment. Here we use these to investigate ‘Spite plateau’ – near-constant lithium abundance observed metal-poor across wide range metallicities (−3 &lt;...
System for mapping of water bodies in Slovenia and its immediate neighbourhood with Sentinel-1 radar satellites have implemented. Algorithms automatically detect presence new data the archive, download data, analyse it, write results, upload them to a web portal. New acquisitions are currently available every six days, but this time will be halved when second starts delivering data.
Abstract GALAH+ is a magnitude-limited survey of high resolution stellar spectra obtained by the HERMES spectrograph at Australian Astronomical Observatory. Its third data release provides reduced with new derivations parameters and abundances 30 chemical elements for 584,015 dwarfs giants, 88 per cent them in Gaia magnitude range 11 &lt; G 14. Here we use these improved values to build library observed which useful study variations individual spectral lines parameters. This other...