Grain growth in newly discovered young eruptive stars

FU Orionis-type stars are young stellar objects showing large outbursts due to highly enhanced accretion from the circumstellar disk onto the protostar. FUor-type outbursts happen in a wide variety of sources from the very embedded ones to those with almost no sign of extended emission beyond the disk. The subsequent eruptions might gradually clear up the obscuring envelope material and drive the protostar on its way to become a disk-only T Tauri star. We used VLT/VISIR to obtain the first spectra that cover the 8-13 $\mu$m mid-infrared wavelength range in low-resolution of five recently discovered FUors. Four objects from our sample show the 10 $\mu$m silicate feature in emission. We study the shape and strength of the silicate feature in these objects and find that they mostly contain large amorphous grains, suggesting that large grains are typically not settled to the midplane in FUor disks. This is a general characteristic of FUors, as opposed to regular T Tauri-type stars whose disks display anything from pristine small grains to significant grain growth. We classify our targets by determining whether the silicate feature is in emission or in absorption, and confront them with the evolutionary scenarios on the dispersal of the envelopes around young stars. In our sample, all Class II objects exhibit silicate emission, while for Class I objects, the appearance of the feature in emission or absorption depends on the viewing angle with respect to the outflow cavity. This highlights the importance of geometric effects when interpreting the silicate feature.Comment: 7 pages, 1 table, 3 figures, accepted for publication in the Astrophysical Journal Letter

Infrared study of transitional disks in Ophiuchus with Herschel

Context. Observations of nearby star-forming regions with the Herschel Space Observatory complement our view of the protoplanetary disks in Ophiuchus with information about the outer disks. Aims. The main goal of this project is to provide new far-infrared fluxes for the known disks in the core region of Ophiuchus and to identify potential transitional disks using data from Herschel. Methods. We obtained PACS and SPIRE photometry of previously spectroscopically confirmed young stellar objects (YSO) in the region and analysed their spectral energy distributions. Results. From an initial sample of 261 objects with spectral types in Ophiuchus, we detect 49 disks in at least one Herschel band. We provide new far-infrared fluxes for these objects. One of them is clearly a new transitional disk candidate. Conclusions. The data from Herschel Space Observatory provides fluxes that complement previous infrared data and that we use to identify a new transitional disk candidate.Comment: 21 pages, with 5 figures. Accepted in Astronomy & Astrophysic

A galaktikus és extragalaktikus háttérsugárzás infravörös vizsgálata = Infrared studies of the galactic and extragalactic background radiation

Kutatásunk célja az ESA csillagászati mesterséges holdja, az Infrared Space Observatory (ISO) 1995. novembere és 1998. áprilisa között végzett 2-240 mikrométeres hullámhosszú háttérméréseinek feldolgozása, a bolygóközi és a galaktikus előtérkomponensek valamint a kozmológiai eredetű extragalaktikus infravörös háttérsugárzás tanulmányozása. Eredményeink: (1) Adatbázisokat állítottunk fel az ISOPHOT legjobb minőségű infravörös háttérméréseiből; (2) Jelentősen javítottuk az ISOPHOT felületi fényesség fotometriájának kalibrációját; (3) Az így újrakalibrált ISOPHOT méréseket szisztematikus összevetettük a COBE/DIRBE hold eredményeivel és kimutattuk, hogy nincs jelentős különbség a két fotometriai rendszer között; (4) Analizáltuk az állatövi fény közép-infravörös színképét. A színkép térbeli változásait pusztán geometriai okokkal magyarázni tudtuk; (5) Kifejlesztettünk egy modellt a kisbolygó populáció infravörös emissziójának statisztikus leírására; (6) Fourier analízis segítségével tanulmányoztuk a galaktikus cirrus emissziójának térbeli szerkezetét, és váratlan függést találtunk a terület abszolút fényességétől; (7) Kimutattuk, hogy a csillagközi por emisszivitása függ a porszemcsék hőmérsékletétől; (8) Elsőként beépítettük az aszteroidák által okozott konfúziós zajt a modellekbe. Az adatbázisaink jelenleg folyó újraprocesszálása új szoftvercsomagunkkal lehetővé teszi a háttérsugárzás komponensekre bontását. | The aim of our project was to collect, calibrate and analyse measurements of the infrared sky brightness obtained by ISOPHOT the photometer on-board ESA's Infrared Space Observatory. Our main results are the following: we (1) built up databases of sky observations using data obtained in the most reliable ISOPHOT observing modes; (2) made significant improvements in the surface brightness calibration of ISOPHOT; (3) compared the surface brightness values with those derived from COBE/DIRBE and showed a good agreement; (4) analysed the mid-infrared spectrum of the zodiacal light, and found that the spatial variations of the spectrum can be explained by geometrical effects (no need for changing dust properties); (5) developed a new model for the statistical description of emission from the asteroidal population; (6) performed Fourier analysis of infrared maps of galactic cirrus clouds and showed that the spectral index unexpectedly depends on the surface brightness; (7) proved that the emissivity of interstellar dust grains changes with temperature; (8) produced confusion noise estimates for different space instruments (asteroidal component is also included). The bulk reprocessing of the sky measurement databases using our new software provides a good basis for the reliable separation of components of the infrared sky brightness

Identification of Young Stellar Object candidates in the GaiaGaia DR2 x AllWISE catalogue with machine learning methods

The second $Gaia$ Data Release (DR2) contains astrometric and photometric data for more than 1.6 billion objects with mean $Gaia$ $G$ magnitude $<$20.7, including many Young Stellar Objects (YSOs) in different evolutionary stages. In order to explore the YSO population of the Milky Way, we combined the $Gaia$ DR2 database with WISE and Planck measurements and made an all-sky probabilistic catalogue of YSOs using machine learning techniques, such as Support Vector Machines, Random Forests, or Neural Networks. Our input catalogue contains 103 million objects from the DR2xAllWISE cross-match table. We classified each object into four main classes: YSOs, extragalactic objects, main-sequence stars and evolved stars. At a 90% probability threshold we identified 1,129,295 YSO candidates. To demonstrate the quality and potential of our YSO catalogue, here we present two applications of it. (1) We explore the 3D structure of the Orion A star forming complex and show that the spatial distribution of the YSOs classified by our procedure is in agreement with recent results from the literature. (2) We use our catalogue to classify published $Gaia$ Science Alerts. As $Gaia$ measures the sources at multiple epochs, it can efficiently discover transient events, including sudden brightness changes of YSOs caused by dynamic processes of their circumstellar disk. However, in many cases the physical nature of the published alert sources are not known. A cross-check with our new catalogue shows that about 30% more of the published $Gaia$ alerts can most likely be attributed to YSO activity. The catalogue can be also useful to identify YSOs among future $Gaia$ alerts.Comment: 19 pages, 12 figures, 3 table

Mid-infrared interferometric variability of DG Tau: implications for the inner-disk structure

Context. DG Tau is a low-mass pre-main sequence star, whose strongly accreting protoplanetary disk exhibits a so-far enigmatic behavior: its mid-infrared thermal emission is strongly time-variable, even turning the 10 $\mu$m silicate feature from emission to absorption temporarily. Aims. We look for the reason for the spectral variability at high spatial resolution and at multiple epochs. Methods. We study the temporal variability of the mid-infrared interferometric signal, observed with the VLTI/MIDI instrument at six epochs between 2011 and 2014. We fit a geometric disk model to the observed interferometric signal to obtain spatial information about the disk. We also model the mid-infrared spectra by template fitting to characterize the profile and time dependence of the silicate emission. We use physically motivated radiative transfer modeling to interpret the mid-infrared interferometric spectra. Results. The inner disk (r<1-3 au) spectra exhibit a 10 $\mu$m absorption feature related to amorphous silicate grains. The outer disk (r>1-3 au) spectra show a crystalline silicate feature in emission, similar to the spectra of comet Hale-Bopp. The striking difference between the inner and outer disk spectral feature is highly unusual among T Tauri stars. The mid-infrared variability is dominated by the outer disk. The strength of the silicate feature changed by more than a factor of two. Between 2011 and 2014 the half-light radius of the mid-infrared-emitting region decreased from 1.15 to 0.7 au. Conclusions. For the origin of the absorption we discuss four possible explanations: a cold obscuring envelope, an accretion heated inner disk, a temperature inversion on the disk surface and a misaligned inner geometry. The silicate emission in the outer disk can be explained by dusty material high above the disk plane, whose mass can change with time, possibly due to turbulence in the disk.Comment: 16 pages, 13 figure

Methodological Investigations on a Neuropteroidea Community

The same Neuropteroidea community was collected and studied in Hungary in the years 1991 and 1992 by using different trapping techniques: a) Malaise trap, b) suction trap, c) yellow pan trap and d) light trap. The studies aimed to compare the different sampling methods for individual species, families and for the whole Neuropteroidea community. In case the whole Neuropteroidea community the trapped individual numbers collected by the suction trap surpassed all other trap types. Relatively high numbers of Neuropteroidea could be collected both by light trap and Malaise traps. The yellow pan traps did not succeed in catching large enough samples neither from point of view of sample size nor from species richness. According to the number of species collected there were not discovered any big difference between the catches of suction trap, Malaise traps and light trap. By evaluating according to families it was stated that in case of the family Raphidiidae the Malaise trap yielded larger and more diverse samples than any other methods; however by increasing the number of yellow pan traps it is possible to augment the number of caught individuals. The suction traps were found very satisfactory in collecting members of the family Coniopterygidae. For the members of the families Hemerobiidae and Chrysopidae both the suction traps and light traps were found effective, although suction traps were more successful in collecting Chrysopidae species. Similarly, by evaluating the data according to individual species it was found that the Malaise traps tended to “under-represent” species belonging to Hemerobius humulinus, Hemerobius Lutescens, Chrysopa pallens and the ones belonging to Chrysoperla carnea complex compared to the suction trap. The opposing situation was perceived with Micromus lanosus and Chrysopa perla. Similarly – compared to suction trap – the light trap significantly “under-represented” the species Hemerobius humulinus, Hemerobius lutescens, Chrysopa pallens, Chrysoperla carnea and Dichochrysa prasina and “over-represented” Micromus angulatus, Sympherobius pygmaeus and Chrysopa phyllochroma. The diversity of Neuropteroidea collected by Malaise trap and light trap surpassed significantly the one of suction trap and yellow pan traps. The assemblages collected by different sampling methods showed some overlapping, but differed in their characters

Pre-protostelláris felhőmagok fizikája = Physics of pre-protostellar cloud cores

Bizonyítottuk, hogy jelentős szerepe van a külső hatásoknak a kistömegű csillagok keletkezésében már a pre-protostelláris felhőmagok kialakulásától kezdve. 1. A Naprendszer 2kpc sugarú környezetében a hideg csillagközi anyag kb. 40%-a van lassú frontok és a csillagközi ionizáló sugárzási tér (trigger) hatása alatt. 2. A csillagközi felhők relatív száma a nyugalomban lévő és külső hatás alatt lévő térrészben hasonló, de a sűrű felhőmagok gyakoribbak a triggerelt csillagközi anyagban. 3. A külső trigger hatások alkalmasak a csillagkeletkezés beindítására a sűrűség fluktuációk megnövelésén keresztül. 4. A trigger esetek száma jelentős, minden harmadik a Naphoz hasonló tömegű fiatal csillag triggerelt csillagközi felhőben születik. További eredményeink: Több mint 10 új felhőmagot azonosítottunk. Felfedeztünk több mint egy tucat új T-asszociációt. A szakirodalomban elsőként felfedeztünk egy keletkező barna törpe jelöltet a Taurusban. Megadtuk a Taurus Molecular Ring szerkezeti és kinematikai leírását. | Trigger mechanisms play an important role in the low mass star formation already in the formation of pre-protostellar cores. 1) As much as 40% of the nearby (within 2kpc) interstellar medium (ISM) mass is exposed to slow interstellar shock fronts, and an enhanced ionizing interstellar radiation field, i.e. the typical trigger mechanisms. 2) Clouds form with the same frequency in the relaxed and in the triggered ISM, but there are far more dense cores in triggered clouds. 3) Triggers like above may turn ISM density enhancements to star forming cloud cores. 4) The triggered fraction of low mass star formation is statistically significant in large Galactic regions, at least 30% of the solar type low mass stars are formed in triggered clouds. Further results: We identified more than a dozen of new cloud cores, and T-associations. A candidate brown dwarf was discovered in Taurus, still in the phase of formation. The Taurus Molecular Ring ISM structure and kinematics was uncovered

A kozmikus por fejlődése a Tejútrendszerben és a távoli Univerzumban = Evolution of cosmic dust in the Milky Way and in the distant Universe

Kutatómunkánk során foglalkoztunk az eredeti munkatervben megjelölt mindhárom témakörrel: a por szerepe és tulajdonságai csillagközi felhőkben, csillagok körüli korongokban, valamint kozmológiai távolságú rendszerekben. Megmutattuk, hogy a sűrű csillagközi felhőkben a porszemcsék optikai tulajdonságai megváltoznak, arra utalva, hogy méretük valamilyen fizikai hatás következtében (összetapadás, jégköpeny képződés) megnő. Az extragalaktikus por tanulmányozására távoli (z <= 1) galaxisokat figyeltünk meg a Spitzer Űrtávcsővel. A legnagyobb hangsúlyt a hirtelen kifényesedést mutató eruptív fiatal csillagok körüli por- és gázkorongok tanulmányozására fektettük. A V1647 Ori kitörése során interferometrikus mérésekkel fel tudtuk bontani a csillagkörüli korong belső részét, és megmutattuk, hogy a kitörés során a belső rész geometriája megváltozik. Az EX Lupi 2008-as kitörését az Európai Déli Obszervatórium és a Spitzer Űrtávcső műszereivel követtük. A kitörés előtt felvett színkép tanúsága szerint az EX Lupit körülvevő korong felszínét kisméretű és amorf szerkezetű por borította, a kitörés csúcsát követően azonban már nagyrészt kristályos porszemcsék spektroszkópiai nyomát láthattuk. Így első ízben sikerült közvetlenül megfigyelni a porszemcsék kristályosodását egy csillagkörüli korongban, lehetséges forgatókönyvet javasolva naprendszerbeli üstökösök anyagának keletkezésére is. A felfedezést a Nature közölte 2009-ben. | We made progress in all three research areas defined in the workplan of the OTKA project: the role and properties of dust in interstellar clouds, in circumstellar disks, and in galaxies at cosmological distances. We demonstrated that the infrared emisivity of the dust particles increases in dense interstellar clouds, suggesting a particle growth via coagulation or the appearance of ice mantels. In order to study the extragalactic dust we performed far-infrared observations of SN Ia host galaxies with the Spitzer Space Telescope. Our most productive research line was, however, the investigation of gas- and dust disks around young eruptive stars. Using interferometric observations, we were able to resolve the inner disk around V1647 Ori, and concluded that the the geometrical structure of the inner part changed during the outburst. The 2008 Jan-Sep eruption of EX Lupi was followed using ESO and Spitzer instruments. Comparing pre-outburst and outburst mid-infrared spectra, we showed that while in quiescence the surface of the disk was dominated by submicron size amorphous particles, during outburst signatures of crystalline dust appeared. It was the first direct detection of on-going crystal formation in a cosmic object, offering also a scenario for the formation of the silicate crystals located in comet nuclei in the Solar System. This result was published in Nature in 2009 May

Study of Neuropteroidea (Raphidioptera, Neuroptera) Communities by Using Malaise Traps in an Untreated Orchard and its Environment

Neuropteroidea communities were studied near Budapest (Nagykovácsi) in an abandoned, mixed orchard and its neighbouring environment: a shrub community without a closed canopy; a shrub level of the canopied oak forest by using Malaise traps. In the open shrub verge of the orchard larger, and in the oak forest more diverse Neuropteroidea community developed than in the other investigated habitats. The Neuropteroidea communities studied did not show stable compositions in the investigated habitats and years. By studying the linkage conditions of different species to different habitats, it was established that Hypochrysa elegans was strongly bound to the shrub level of the closed oak forest. Besides that, both in the shrub level and in the open forest edge, the species Micromus lanosus, Micromus angulatus, Hemerobius micans, Hemerobius lutescens and Hemerobius humulinus were found with higher density. The species Dichrostigma flavipes, Chrysopa formosa, Chrysopa perla, Xanthostigma xanthostigma, Chrysoperla carnea and Dichochrysa prasina occurred in all three habitats, thus they have to be regarded as habitat generalists. By passing beyond these tendencies Dichrostigma flavipes, Chrysopa formosa and Chrysopa perla seemed to be more attached to the shrubby edge

Game semantic analysis of equivalence in IMJ

Using game semantics, we investigate the problem of verifying contextual equivalences in Interface Middleweight Java (IMJ), an imperative object calculus in which program phrases are typed using interfaces. Working in the setting where data types are non-recursive and restricted to finite domains, we identify the frontier between decidability and undecidability by reference to the structure of interfaces present in typing judgments. In particular, we show how to determine the decidability status of problem instances (over a fixed type signature) by examining the position of methods inside the term type and the types of its free identifiers. Our results build upon the recent fully abstract game semantics of IMJ. Decidability is proved by translation into visibly pushdown register automata over infinite alphabets with fresh-input recognition