On the Relationship Between Debris Disks and Planets

Dust in debris disks is generated by collisions among planetesimals. The existence of these planetesimals is a consequence of the planet formation process, but the relationship between debris disks and planets has not been clearly established. Here we analyze Spitzer/MIPS 24 and 70 μm data for 150 planet-bearing stars, and compare the incidence of debris disks around these stars with a sample of 118 stars around which planets have been searched for, but not found. Together they comprise the largest sample ever assembled to deal with this question. The use of survival analysis techniques allows us to account for the large number of nondetections at 70 μm. We discovered 10 new debris disks around stars with planets and one around a star without known planets. We found that the incidence of debris disks is marginally higher among stars with planets, than among those without, and that the brightness of the average debris disk is not significantly different in the two samples. We conclude that the presence of a planet that has been detected via current radial velocity techniques is not a good predictor of the presence of a debris disk detected at infrared wavelengths

Dust Spreading in Debris Discs: Do Small Grains Cling on to Their Birth Environment?

Debris discs are dusty belts of planetesimals around main-sequence stars, similar to the asteroid and Kuiper belts in our solar system. The planetesimals cannot be observed directly, yet they produce detectable dust in mutual collisions. Observing the dust, we can try to infer properties of invisible planetesimals. Here we address the question of what is the best way to measure the location of outer planetesimal belts that encompass extrasolar planetary systems. A standard method is using resolved images at mm-wavelengths, which reveal dust grains with sizes comparable to the observational wavelength. Smaller grains seen in the infrared (IR) are subject to several non-gravitational forces that drag them away from their birth rings, and so may not closely trace the parent bodies. In this study, we examine whether imaging of debris discs at shorter wavelengths might enable determining the spatial location of the exo-Kuiper belts with sufficient accuracy. We find that around M-type stars the dust best visible in the mid-IR is efficiently displaced inward from their birth location by stellar winds, causing the discs to look more compact in mid-IR images than they actually are. However, around earlier-type stars where the majority of debris discs is found, discs are still the brightest at the birth ring location in the mid-IR regime. Thus, sensitive IR facilities with good angular resolution, such as MIRI on JWST, will enable tracing exo-Kuiper belts in nearby debris disc systems.Comment: 16 page

Physical conditions of gas components in debris disks of 49 Ceti and HD 21997

Characterization of gas component in debris disks is of fundamental importance for understanding its origin. Toward this goal, we have conducted non-LTE (local thermodynamic equilibrium) analyses of the rotational spectral lines of CO including those of rare isotopologues ($^{13}$CO and C$^{18}$O) observed toward the gaseous debris disks of 49 Ceti and HD 21997 with the Atacama Large Millimeter/submillimeter Array (ALMA) and Atacama Compact Array (ACA). The analyses have been carried out for a wide range of the H$_{2}$ density, and the observed line intensities are found to be reproduced, as far as the H$_{2}$ density is higher than 10$^{3}$ cm$^{-3}$. The CO column density and the gas temperature are evaluated to be (1.8-5.9)$\times$10$^{17}$ cm$^{-2}$ and 8-11 K for 49 Ceti and (2.6-15)$\times$10$^{17}$ cm$^{-2}$ and 8-12 K for HD 21997, respectively, where the H$_{2}$ collision is assumed for the rotational excitation of CO. The results do not change significantly even if electron collision is considered. Thus, CO molecules can be excited under environments of no H$_{2}$ or a small number of H$_{2}$ molecules, even where the collision with CO, C, O, and C$^{+}$ would make an important contribution for the CO excitation in addition to H$_{2}$. Meanwhile, our result does not rule out the case of abundant H$_{2}$ molecules. The low gas temperature observed in the debris disks is discussed in terms of inefficient heating by interstellar and stellar UV radiation.Comment: 25 pages, 5 figures, 9 tables, accepted for publication in Ap

The young star population of L1188

We present new results on the young star population of the Lynds~1188 molecular cloud, associated with the Cepheus Bubble, a giant interstellar shell around the association Cep~OB\,2. In order to reveal the star-forming scenario of the molecular cloud located on the supershell, and understand the history of star formation in the region, we identified and characterized young star candidates based on an H$\alpha$ emission survey and various published photometric datasets. Using Gaia DR2 astrometry we studied the spatial distribution of the young star candidates and isolated three groups based on their distances. We constructed spectral energy distributions of our target stars, based on Pan-STARRS, 2MASS, {\it Spitzer} and {\it WISE} photometric data, estimating their spectral types, extinctions, and luminosities. We estimated masses by means of pre-main-sequence evolutionary models, and derived accretion rates from the equivalent width of the H$\alpha$ line. We studied the structure of the cloud by constructing a new extinction map, based on Pan-STARRS data. Our results show that the distribution of low-mass young stars in L1188 is well correlated with that of the dust and mole\-cular gas. We identified two small, compact clusters and a loose aggregate of young stars. We found that star formation in L1188 started about 5 million years ago. The apparent age gradient of young stars across the cloud and the ammonia cores located to the east of the optically visible young stellar groups support the scenario of star formation propagating away from the centre of the Cepheus Bubble.Comment: 19 pages, 11 figures, accepted for publication in MNRA

Mid-infrared Variability of the Neutrino Source Blazar TXS 0506+056

The IceCube instrument detected a high-energy cosmic neutrino event on 2017 September 22 (IceCube_170922A, IceCube Collaboration 2018), which the electromagnetic follow-up campaigns associated with the flaring $\gamma$-ray blazar TXS 0506$+$056 (e.g., Padovani et al., 2018). We investigated the mid-infrared variability of the source by using the available single exposure data of the WISE satellite at $3.4$ and $4.6\mu$m. TXS 0506$+$056 experienced a $\sim 30$% brightening in both of these bands a few days prior to the neutrino event. Additional intraday infrared variability can be detected in 2010. Similar behaviour seen previously in $\gamma$-ray bright radio-loud AGN has been explained by their jet emission (e.g., Jiang et al. 2012).Comment: 3 pages, 1 figure; accepted by the Research Notes of the American Astronomical Societ

Nap típusú csillagok korai fejlődési szakaszainak vizsgálata = Study of early evolutionary stages of Solar type stars

1. A V1647 Ori 2004. januártól 2005. októberig tartó kitörését nemzetközi együttműködéssel, több műszerrel követtük. Analizáltuk a csillag fényességének és színképvonalainak változását a kitörés alatt, és infravörösben az elhalványodás után is, egészen 2006. szeptemberéig. 2. Nap típusú fiatal csillagokat és protocsillagokat azonosítottunk a Lynds 1333, Lynds 1622, Lynds 1340 közeli molekulafelhőkben és a Cepheus flare óriás molekulafelhő-komplexum mintegy 200 négyzetfoknyi területén. Az objektumok nagy része korábban nem ismert fiatal csillag. Saját spektroszkópiai és fotometriai méréseink alapján meghatároztuk a fiatal csillagok spektráltípusát, luminozitását, tömegét és korát. Középinfravörös (Spitzer Space Telescope) adatbázis alapján vizsgáltuk az akkréciós korongjaik tulajdonságait, ezek környezetfüggését. 3. A Spitzer Space Telescope középinfravörös adatainak feldolgozásával vizsgáltuk az NGC 2244 fiatal nyílthalmaz szerkezetét és a halmaztagok akkréciós korongjainak tulajdonságait. 337 fősorozat előtti csillagot és 25 I osztályú protocsillagot azonosítottunk. Spitzer és HST mérések alapján elemeztük a por elpárolgásának folyamatát a forró csillagok közelében. A h és chi Persei Spitzer-adatainak elemzésével megállapítottuk, hogy a 24 mikronon megfigyelhető törmelékkorongok tipikus kora 5 és 15 millió év között van. 4. A pályázat támogatásával elkészült egy kis felbontású spektrográf a piszkés-tetői RCC teleszkópra. | 1. We followed the outburst of V1647 Ori between 2004 January and 2005 October using several instruments. We analysed the variations of the brightness and spectral line intensities during the outburst, and even after the dimming of the star in the infrared, up to 2006 September. 2. We identified Solar type young stars and protostars in the nearby molecular clouds Lynds 1333, Lynds 1622, as well as over the whole surface of some 200 square degrees of the Cepheus flare molecular complex. Most of the objects are newly identified young stars. Based on our own spectroscopic and photometric observations we determined the spectral types, luminosities, masses, and ages of the stars. Based on the mid-infrared Spitzer Space Telescope archive data we studied their accretion disks, and the dependence of disk properties on the environment. 3. We studied the structure of the young open cluster NGC 2244 based on the mid-infrared data obtained by the Spitzer Space Telescope. We identified 337 pre-main sequence stars and 25 Class I protostars. Based on Spitzer and HST measurements we analysed the evaporation of the dust in the vicinity of hot stars. Based on Spitzer observations of the open cluster h and chi Persei we established that the typical age of the debris disks observed at 24 micron is 5-15 million years. 4. A low-resolution spectrograph has been devised and built for the RCC telescope with the support of this project

Infrared variability of radio-loud narrow-line Seyfert 1 galaxies

Most of the radio-loud narrow-line Seyfert 1 (NLS1) galaxies resemble compact steep-spectrum sources. However, the extremely radio-loud ones show blazar-like characteristics, like flat radio spectra, compact radio cores, substantial variability and high brightness temperatures. These objects are thought to be similar to blazars as they possess relativistic jets seen at small angle to the line of sight. This claim has been further supported by the Fermi satellite discovery of gamma-ray emission from a handful of these sources. Using the Wide-Field Infrared Survey Explorer (WISE) data, we analyzed the mid-infrared variability characteristics of $42$ radio-loud NLS1 at $3.4$ and $4.6\,\mu$m. We found that $27$ out of the studied $42$ sources showed variability in at least one of the two infrared bands. In some cases, significant changes in the infrared colors can alter the location of the source in the WISE color-color diagram which might lead to different classification. More than $60$% of the variable sources also showed variability within a $1-1.5$ day interval. Such short time scales argue for a compact emission region like those associated with the jets. This connection is further strengthened by the fact that the brightest $\gamma$-ray emitters of the sample ($6$ sources), all showed short time scale infrared variability.Comment: Accepted for publication in Proceedings of Science for the conference "Revisiting narrow-line Seyfert 1 galaxies and their place in the Universe" (Padova, April 2018

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