arXiv subjects

A. Moór

Publications and source records attributed to A. Moór.

At least 55 records · Page 3Linked to original sources

arXiv2016

Far-infrared photometric observations of the outer planets and satellites with Herschel-PACS

We present all Herschel PACS photometer observations of Mars, Saturn, Uranus, Neptune, Callisto, Ganymede, and Titan. All measurements were carefully inspected for quality problems, were reduced in a (semi-)standard way, and were calibrated. The derived flux densities are tied to the standard PACS photometer response calibration, which is based on repeated measurements of five fiducial stars. The overall absolute flux uncertainty is dominated by the estimated 5% model uncertainty of the stellar models in the PACS wavelength range between 60 and 210 micron. A comparison with the corresponding planet and satellite models shows excellent agreement for Uranus, Neptune, and Titan, well within the specified 5%. Callisto is brighter than our model predictions by about 4-8%, Ganymede by about 14-21%. We discuss possible reasons for the model offsets. The measurements of these very bright point-like sources, together with observations of stars and asteroids, show the high reliability of the PACS photometer observations and the linear behavior of the PACS bolometer source fluxes over more than four orders of magnitude (from mJy levels up to more than 1000 Jy). Our results show the great potential of using the observed solar system targets for cross-calibration purposes with other ground-based, airborne, and space-based instruments and projects. At the same time, the PACS results will lead to improved model solutions for future calibration applications.

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arXiv2015

Light curves of the latest FUor: Indication of a close binary

We monitored the recent FUor 2MASS J06593158-0405277 (V960 Mon) since November 2009 at various observatories and multiple wavelengths. After the outburst by nearly 2.9 mag in $r$ around September 2014 the brightness gently fades until April 2015 by nearly 1 mag in $U$ and 0.5 mag in $z$. Thereafter the brightness at $λ>5000 Å$ was constant until June 2015 while the shortest wavelengths ($U, B$) indicate a new rise, similar to that seen for the FUor V2493 Cyg (HBC722). Our near-infrared (NIR) monitoring between December 2014 and April 2015 shows a smaller outburst amplitude ($\sim$2 mag) and a smaller (0.2 $-$ 0.3 mag) post-outburst brightness decline. Optical and NIR color-magnitude diagrams indicate that the brightness decline is caused by growing extinction. The post-outburst light curves are modulated by an oscillating color-neutral pattern with a period of about 17 days and an amplitude declining from $\sim$0.08 mag in October 2014 to $\sim$0.04 mag in May 2015. The properties of the oscillating pattern lead us to suggest the presence of a close binary with eccentric orbit.

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arXiv2015

Discovery of molecular gas around HD 131835 in an APEX molecular line survey of bright debris disks

Debris disks are considered to be gas-poor, but recent observations revealed molecular or atomic gas in several 10-40 Myr old systems. We used the APEX and IRAM 30m radiotelescopes to search for CO gas in 20 bright debris disks. In one case, around the 16 Myr old A-type star HD 131835, we discovered a new gas-bearing debris disk, where the CO 3-2 transition was successfully detected. No other individual system exhibited a measurable CO signal. Our Herschel Space Observatory far-infrared images of HD 131835 marginally resolved the disk both at 70 and 100$μ$m, with a characteristic radius of ~170 au. While in stellar properties HD 131835 resembles $β$ Pic, its dust disk properties are similar to those of the most massive young debris disks. With the detection of gas in HD 131835 the number of known debris disks with CO content has increased to four, all of them encircling young ($\leq$40 Myr) A-type stars. Based on statistics within 125 pc, we suggest that the presence of detectable amount of gas in the most massive debris disks around young A-type stars is a common phenomenon. Our current data cannot conclude on the origin of gas in HD 131835. If the gas is secondary, arising from the disruption of planetesimals, then HD 131835 is a comparably young and in terms of its disk more massive analogue of the $β$ Pic system. However, it is also possible that this system similarly to HD 21997 possesses a hybrid disk, where the gas material is predominantly primordial, while the dust grains are mostly derived from planetesimals.

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arXiv2015

Debris Disks in Nearby Young Moving Groups in the ALMA Era

Many members of nearby young moving groups exhibit infrared excess attributed to circumstellar debris dust, formed via erosion of planetesimals. With their proximity and well-dated ages, these groups are excellent laboratories for studying the early evolution of debris dust and of planetesimal belts. ALMA can spatially resolve the disk emission, revealing the location and extent of these belts, putting constraints on planetesimal evolution models, and allowing us to study planet-disk interactions. While the main trends of dust evolution in debris disks are well-known, there is almost no information on the evolution of gas. During the transition from protoplanetary to debris state, even the origin of gas is dubious. Here we review the exciting new results ALMA provided by observing young debris disks, and discuss possible future research directions.

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arXiv2015

Overtone and multi-mode RR Lyrae stars in the globular cluster M3

The overtone and multi-mode RR Lyrae stars in the globular cluster M3 are studied using a 200-d long, $B,V$ and $I_{\mathrm C}$ time-series photometry obtained in 2012. 70\% of the 52 overtone variables observed show some kind of multi-periodicity (additional frequency at ${f_{0.61}}={f_{\mathrm {1O}}}/0.61$ frequency ratio, Blazhko effect, double/multi-mode pulsation, period doubling). A signal at 0.587 frequency ratio to the fundamental-mode frequency is detected in the double-mode star, V13, which may be identified as the second radial overtone mode. If this mode-identification is correct, than V13 is the first RR Lyrae star showing triple-mode pulsation of the first three radial modes. Either the Blazhko effect or the ${f_{0.61}}$ frequency (or both of these phenomena) appear in 7 double-mode stars. The $P_{\mathrm{1O}}/P_{\mathrm{F}}$ period ratio of RRd stars showing the Blazhko effect are anomalous. A displacement of the main frequency component at the fundamental-mode with the value of modulation frequency (or its half) is detected in three Blazhko RRd stars parallel with the appearance of the overtone-mode pulsation. The ${f_{0.61}}$ frequency appears in RRc stars that lie at the blue side of the double-mode region and in RRd stars, raising the suspicion that its occurrence may be connected to double-mode pulsation. The changes of the Blazhko and double-mode properties of the stars are also reviewed using the recent and archive photometric data.

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arXiv2015

The progenitor of the FUor-type young eruptive star 2MASS J06593158-0405277

Only a dozen confirmed FU Orionis-type young outbursting stars (FUors) are known today; this explains the interest in the recent FUor eruption of 2MASS J06593158-0405277. Its outburst and expected decline will be subject to numerous studies in the future. Almost equally important for the understanding of the eruption mechanism, however, is the physical characterization of the FUor's precursor. Here we analyze unpublished archival data and summarize - and partly revise - all relevant photometry from optical to submillimeter wavelengths. Our analysis implies that the FUor is possibly associated with eight T Tauri star candidates and a strong Class 0 source. Adopting a distance of 450 pc for the FUor, we derive a quiescent bolometric luminosity and temperature of L_bol = 4.8 L_Sun and T_bol = 1190 K, typical for young Class II sources. The central star has a temperature of T_eff = 4000 K, a mass of 0.75 M_Sun, and an age of about 6 x 10^5 yr. The SED implies a circumstellar mass of 0.01 - 0.06 M_Sun, and the system is surrounded by a faint infrared nebulosity. Our results provide an almost complete picture of a FUor progenitor, supporting the interpretation of future post-outburst studies.

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arXiv2014

Stirring in massive, young debris discs from spatially resolved Herschel images

A significant fraction of main-sequence stars are encircled by dusty debris discs, where the short-lived dust particles are replenished through collisions between planetesimals. Most destructive collisions occur when the orbits of smaller bodies are dynamically stirred up, either by the gravitational effect of locally formed Pluto-sized planetesimals (self-stirring scenario), or via secular perturbation caused by an inner giant planet (planetary stirring). The relative importance of these scenarios in debris systems is unknown. Here we present new Herschel Space Observatory imagery of 11 discs selected from the most massive and extended known debris systems. All discs were found to be extended at far-infrared wavelengths, five of them being resolved for the first time. We evaluated the feasibility of the self-stirring scenario by comparing the measured disc sizes with the predictions of the model calculated for the ages of our targets. We concluded that the self-stirring explanation works for seven discs. However, in four cases, the predicted pace of outward propagation of the stirring front, assuming reasonable initial disc masses, was far too low to explain the radial extent of the cold dust. Therefore, for HD 9672, HD 16743, HD 21997, and HD 95086, another explanation is needed. We performed a similar analysis for ß Pic and HR 8799, reaching the same conclusion. We argue that planetary stirring is a promising possibility to explain the disk properties in these systems. In HR 8799 and HD 95086 we may already know the potential perturber, since their known outer giant planets could be responsible for the stirring process. Our study demonstrates that among the largest and most massive debris discs self-stirring may not be the only active scenario, and potentially planetary stirring is responsible for destructive collisions and debris dust production in a number of systems.

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arXiv2014

New Candidate Eruptive Young Stars in Lynds 1340

We report on the discovery of three candidate eruptive young stars, found during our comprehensive multi-wavelength study of the young stellar population of the dark cloud L1340. These stars are as follows. (1) IRAS 02224+7227 (2MASS 02270555+7241167, HH 487 S) exhibited FUor-like spectrum in our low-resolution optical spectra. The available photometric data restrict its luminosity to 23 L_sun < L_bol < 59 L_sun. (2) 2MASS 02263797+7304575, identified as a classical T Tauri star during our H alpha survey, exhibited an EXor type brightening in 2005 November, at the time of the SDSS observations of the region. (3) 2MASS 02325605+7246055, a low-mass embedded young star, associated with a fan-shaped infrared nebula, underwent an outburst between the DSS1 and DSS2 surveys, leading to the appearance of a faint optical nebula. Our [SII] and H alpha images, as well as the Spitzer IRAC 4.5 micron images revealed Herbig-Haro objects associated with this star. Our results suggest that amplitudes and time scales of outbursts do not necessarily correlate with the evolutionary stage of the stars.

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arXiv2014

Magnitude-range brightness variations of overactive K giants

We study three representative, overactive spotted K giants (IL Hya, XX Tri, and DM UMa) known to exhibit V-band light variations between 0.65-1.05 mags. Our aim is to find the origin of their large brightness variation. We employ long-term phase-resolved multicolor photometry, mostly from automatic telescopes, covering 42 yr for IL Hya, 28 yr for XX Tri, and 34 yr for DM UMa. For one target, IL Hya, we present a new Doppler image from NSO data taken in late 1996. Effective temperatures for our targets are determined from all well-sampled observing epochs and are based on a V-I_C color-index calibration. The effective temperature change between the extrema of the rotational modulation for IL Hya and XX Tri is in the range 50-200 K. The bolometric flux during maximum of the rotational modulation, i.e., the least spotted states, varied by up to 39% in IL Hya and up to 54% in XX Tri over the course of our observations. We emphasize that for IL Hya this is just about half of the total luminosity variation that can be explained by the photospheric temperature (spots/faculae) changes, while for XX Tri it is even about one third. The long-term, 0.6 mag V-band variation of DM UMa is more difficult to explain because little or no B-V color index change is observed on the same timescale. Placing the three stars with their light and color variations into H-R diagrams, we find that their overall luminosities are generally too low compared to predictions from current evolutionary tracks. A change in the stellar radius due to strong and variable magnetic fields during activity cycles likely plays a role in explaining the anomalous brightness and luminosity of our three targets. At least for IL Hya, a radius change of about 9% is suggested from m_bol and T_eff, and is supported by independent vsin(i) measurements.

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arXiv2013

Radial velocity variations in the young eruptive star EX Lup

EX Lup-type objects (EXors) are low-mass pre-main sequence objects characterized by outbursts attributed to highly enhanced disk accretion. The trigger mechanism of EXor outbursts is still debated. One theory requires a close (sub)stellar companion that perturbs the inner disk and triggers the onset of the outburst. Here, we study the radial velocity (RV) variations of EX Lup, the prototype of EXors. We conducted a 5-year RV survey with HARPS and FEROS. We analyzed the activity of EX Lup by checking the bisector and several other activity indicators. We complemented the RV data with photometric monitoring to look for signatures of activity or varying accretion. We found that the RV of EX Lup is periodic, with stable period, semi-amplitude, and phase over at least four years of observations. This period is not present in any of the activity indicators. However, the RV of narrow metallic emission lines suggest the same period, but with an anti-correlating phase. The observed absorption line RVs can be fitted with a Keplerian solution around a 0.6 M_Sun central star with M2 sin i = (14.7 +/- 0.7) M_Jup and eccentricity of e = 0.24. Alternatively, we attempted to model the observations with a cold/hot stellar spot as well, but the spot parameters needed to reproduce the RV semi-amplitude are in contradiction with the photometric variability, making the spot scenario unlikely. We discuss two possibilities to explain the RV data: a geometry with two accretion columns rotating with the star, and a single accretion flow synchronized with the orbital motion of the hypothetical companion. In the companion scenario, the companion's mass would fall into the brown dwarf desert, which, together with the unusually small separation would make EX Lup a unique binary system, with interesting implications on the physical mechanisms responsible for triggering the outburst.

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arXiv2013

ALMA observations of the molecular gas in the debris disk of the 30 Myr old star HD 21997

The 30 Myr old A3-type star HD 21997 is one of the two known debris dust disks having a measurable amount of cold molecular gas. With the goal of understanding the physical state, origin, and evolution of the gas in young debris disks, we obtained CO line observations with the Atacama Large Millimeter/submillimeter Array (ALMA). Here we report on the detection of 12CO and 13CO in the J=2-1 and J=3-2 transitions and C18O in the J=2-1 line. The gas exhibits a Keplerian velocity curve, one of the few direct measurements of Keplerian rotation in young debris disks. The measured CO brightness distribution could be reproduced by a simple star+disk system, whose parameters are r_in < 26 AU, r_out = 138 +/- 20 AU, M_*=1.8 +0.5 -0.2 M_Sun, and i = 32.6 +/- 3.1 degrees. The total CO mass, as calculated from the optically thin C18O line, is about (4-8) x 10^-2 M_Earth, while the CO line ratios suggest a radiation temperature on the order of 6-9 K. Comparing our results with those obtained for the dust component of the HD 21997 disk from the ALMA continuum observations by Moór et al., we conclude that comparable amounts of CO gas and dust are present in the disk. Interestingly, the gas and dust in the HD 21997 system are not co-located, indicating a dust-free inner gas disk within 55 AU of the star. We explore two possible scenarios for the origin of the gas. A secondary origin, which involves gas production from colliding or active planetesimals, would require unreasonably high gas production rates and would not explain why the gas and dust are not co-located. We propose that HD 21997 is a hybrid system where secondary debris dust and primordial gas coexist. HD 21997, whose age exceeds both the model predictions for disk clearing and the ages of the oldest T Tauri-like or transitional gas disks in the literature, may be a key object linking the primordial and the debris phases of disk evolution.

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arXiv2013

ALMA continuum observations of a 30 Myr old gaseous debris disk around HD 21997

Circumstellar disks around stars older than 10 Myr are expected to be gas-poor. There are, however, two examples of old (30-40 Myr) debris-like disks containing a detectable amount of cold CO gas. Here we present ALMA and Herschel Space Observatory observations of one of these disks, around HD 21997, and study the distribution and origin of the dust and its connection to the gas. Our ALMA continuum images at 886um clearly resolve a broad ring of emission within a diameter of ~4.5 arcsec, adding HD 21997 to the dozen debris disks resolved at (sub)millimeter wavelengths. Modeling the morphology of the ALMA image with a radiative transfer code suggests inner and outer radii of ~55 and ~150 AU, and a dust mass of 0.09 M_Earth. Our data and modeling hints at an extended cold outskirt of the ring. Comparison with the morphology of the CO gas in the disk reveals an inner dust-free hole where gas nevertheless can be detected. Based on dust grain lifetimes, we propose that the dust content of this gaseous disk is of secondary origin produced by planetesimals. Since the gas component is probably primordial, HD 21997 is one of the first known examples of a hybrid circumstellar disk, a so-far little studied late phase of circumstellar disk evolution.

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arXiv2013

PACS photometer calibration block analysis

The absolute stability of the PACS bolometer response over the entire mission lifetime without applying any corrections is about 0.5% (standard deviation) or about 8% peak-to-peak. This fantastic stability allows us to calibrate all scientific measurements by a fixed and time-independent response file, without using any information from the PACS internal calibration sources. However, the analysis of calibration block observations revealed clear correlations of the internal source signals with the evaporator temperature and a signal drift during the first half hour after the cooler recycling. These effects are small, but can be seen in repeated measurements of standard stars. From our analysis we established corrections for both effects which push the stability of the PACS bolometer response to about 0.2% (stdev) or 2% in the blue, 3% in the green and 5% in the red channel (peak-to-peak). After both corrections we still see a correlation of the signals with PACS FPU temperatures, possibly caused by parasitic heat influences via the Kevlar wires which connect the bolometers with the PACS Focal Plane Unit. No aging effect or degradation of the photometric system during the mission lifetime has been found.

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arXiv2013

What is the difference? Blazhko and non-Blazhko RRab stars and the special case of V123 in M3

In an extended photometric campaign of RR Lyrae variables of the globular cluster M3, an aberrant light-curve, non-Blazhko RRab star, V123, was detected. Based on its brightness, colors and radial velocity curve, V123 is a bona fide member of M3. The light curve of V123 exhibits neither a bump preceding light minimum, nor a hump on the rising branch, and has a longer than normal rise time, with a convex shape. Similar shape characterizes the mean light curves of some large-modulation-amplitude Blazhko stars, but none of the regular RRab variables with similar pulsation periods. This peculiar object thus mimics Blazhko variables without showing any evidence of periodic amplitude and/or phase modulation. We cannot find any fully convincing answer to the peculiar behavior of V123, however, the phenomenon raises again the possibility that rotation and aspect angle might play a role in the explanation of the Blazhko phenomenon, and some source of inhomogeneity acts (magnetic field, chemical inhomogeneity) that deforms the radial pulsation of Blazhko stars during the modulation.

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arXiv2013

Dense cores in the dark cloud complex LDN1188

We present a molecular line emission study of the LDN1188 dark cloud complex located in Cepheus. In this work we focused on the densest parts of the cloud and on the close neighbourhood of infrared point sources. We made ammonia mapping with the Effelsberg 100-m radio telescope and identified 3 dense cores. CS(1--0), CS(2--1) and HCO$^{+}$(1--0) measurements performed with the Onsala 20\,m telescope revealed the distribution of dense molecular material. The molecular line measurements were supplemented by mapping the dust emission at 1.2\,mm in some selected directions using the IRAM 30\,m telescope. With these data we could work out a likely evolutionary sequence in this dark clould complex.

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arXiv2013

A resolved debris disk around the candidate planet-hosting star HD95086

Recently, a new planet candidate was discovered on direct images around the young (10-17 Myr) A-type star HD95086. The strong infrared excess of the system indicates that, similarly to HR8799, ß Pic, and Fomalhaut, the star harbors a circumstellar disk. Aiming to study the structure and gas content of the HD95086 disk, and to investigate its possible interaction with the newly discovered planet, here we present new optical, infrared and millimeter observations. We detected no CO emission, excluding the possibility of an evolved gaseous primordial disk. Simple blackbody modeling of the spectral energy distribution suggests the presence of two spatially separate dust belts at radial distances of 6 and 64 AU. Our resolved images obtained with the Herschel Space Observatory reveal a characteristic disk size of ~6.0x5.4 arcsec (540x490 AU) and disk inclination of ~25 degree. Assuming the same inclination for the planet candidate's orbit, its re-projected radial distance from the star is 62 AU, very close to the blackbody radius of the outer cold dust ring. The structure of the planetary system at HD95086 resembles the one around HR8799. Both systems harbor a warm inner dust belt and a broad colder outer disk and giant planet(s) between the two dusty regions. Modelling implies that the candidate planet can dynamically excite the motion of planetesimals even out to 270 AU via their secular perturbation if its orbital eccentricity is larger than about 0.4. Our analysis adds a new example to the three known systems where directly imaged planet(s) and debris disks co-exist.

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arXiv2013

Unveiling new members in five nearby young moving groups

In the last decade many kinematic groups of young stars (<100 Myr) were discovered in the solar neighbourhood. Since the most interesting period of planet formation overlaps with the age of these groups, their well dated members are attractive targets for exoplanet searches by direct imaging. We combined astrometric, photometric and X-ray data, and applied strict selection criteria to explore the stellar content of five nearby moving groups. We identified more than 100 potential new candidate members in the ß Pic moving group, and in the Tucana-Horologium, Columba, Carina, and Argus associations. In order to further assess and confirm their membership status, we analysed radial velocity data and lithium equivalent widths extracted from high-resolution spectra of 54 candidate stars. We identified 35 new probable/possible young moving group members: 4 in the ß Pic moving group, 11 in the Columba association, 16 in the Carina association, and 4 in the Argus association. We found serendipitiously a new AB Dor moving group member as well. For four Columba systems Hipparcos based parallaxes have already been available and as they are consistent with the predicted kinematic parallaxes, they can be considered as secure new members.

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arXiv2013

Exploring the circumstellar environment of the young eruptive star V2492 Cyg

Context. V2492 Cyg is a young eruptive star that went into outburst in 2010. The near-infrared color changes observed since the outburst peak suggest that the source belongs to a newly defined sub-class of young eruptive stars, where time-dependent accretion and variable line-of-sight extinction play a combined role in the flux changes. Aims. In order to learn about the origin of the light variations and to explore the circumstellar and interstellar environment of V2492 Cyg, we monitored the source at ten different wavelengths, between 0.55 μm and 2.2 μm from the ground and between 3.6 μm and 160 μm from space. Methods. We analyze the light curves and study the color-color diagrams via comparison with the standard reddening path. We examine the structure of the molecular cloud hosting V2492 Cyg by computing temperature and optical depth maps from the far-infrared data. Results. We find that the shapes of the light curves at different wavelengths are strictly self-similar and that the observed variability is related to a single physical process, most likely variable extinction. We suggest that the central source is episodically occulted by a dense dust cloud in the inner disk, and, based on the invariability of the far-infrared fluxes, we propose that it is a long-lived rather than a transient structure. In some respects, V2492 Cyg can be regarded as a young, embedded analog of UX Orionis-type stars. Conclusions. The example of V2492 Cyg demonstrates that the light variations of young eruptive stars are not exclusively related to changing accretion. The variability provided information on an azimuthally asymmetric structural element in the inner disk. Such an asymmetric density distribution in the terrestrial zone may also have consequences for the initial conditions of planet formation.

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