8 research outputs found
Spectral Evolution and Radial Dust Transport in the Prototype Young Eruptive System EX Lup
EX Lup is the prototype of a class of pre-main sequence eruptive stars
defined by their repetitive outbursts lasting several months. In 2008
January-September EX Lup underwent its historically largest outburst,
brightening by about 4 magnitudes in visual light. In previous studies we
discovered on-going silicate crystal formation in the inner disk during the
outburst, but also noticed that the measured crystallinity fraction started
decreasing after the source returned to the quiescent phase. Here we present
new observations of the 10 m silicate feature, obtained with the MIDI and
VISIR instruments at Paranal Observatory. The observations demonstrate that
within five years practically all crystalline forsterite disappeared from the
surface of the inner disk. We reconstruct this process by presenting a series
of parametric axisymmetric radiative transfer models of an expanding dust cloud
that transports the crystals from the terrestrial zone to outer disk regions
where comets are supposed to form. Possibly the early Sun also experienced
similar flare-ups, and the forming planetesimals might have incorporated
crystalline silicate material produced by such outbursts. Finally, we discuss
how far the location of the dust cloud could be constrained by future JWST
observations.Comment: 12 pages, 4 figures, accepted for publication in Ap
Simultaneous H alpha and dust reverberation mapping of 3C120: Testing the bowl-shaped torus geometry
At the Universitaetssternwarte Bochum near Cerro Armazones we have monitored
the Seyfert-1 galaxy 3C 120 between September 2014 and March 2015 in BVRI and a
narrow band filter covering the redshifted H alpha line; in addition we
obtained a single con-temporary spectrum with FAST at Mt. Hopkins. Compared to
earlier epochs 3C 120 is about a factor of three brighter, allowing us to study
the shape of the broad line region (BLR) and the dust torus in a high
luminosity phase. The analysis of the light curves yields that the dust echo is
rather sharp and symmetric in contrast to the more complex broad H alpha BLR
echo. We investigate how far this supports an optically thick bowl-shaped BLR
and dust torus geometry as proposed by Kawaguchi & Mori (2010) and Goad et al.
(2012). The comparison with several parameterizations of these models supports
the following geometry: the BLR clouds lie inside the bowl closely above the
bowl rim, up to a half covering angle 0 deg < theta < 40 deg (measured against
the equatorial plane). Then the BLR is spread over many isodelay surfaces,
yielding a smeared and structured echo as observed. Furthermore, if the BLR
clouds shield the bottom of the bowl rim against radiation from the nucleus,
the hot dust emission comes essentially from the top edge of the bowl (40 deg <
theta < 45 deg). Then, for small inclinations as for 3C120, the top dust edge
forms a ring which largely coincides with a narrow range of isodelay surfaces,
yielding the observed sharp dust echo. The scale height of the BLR increases
with radial distance from the black hole. This leads to luminosity dependent
foreshortening effects of the lag. We discuss implications and possible
corrections of the foreshortening for the black hole mass determination and
consequences for the lag (size) - luminosity relationships and the difference
to interferometric torus sizes.Comment: 17 pages, 18 figures, 3 tables, accepted for publication in in
section 4. Extragalactic astronomy of Astronomy and Astrophysic
Time delay measurement of Mg II line in CTS C30.10 with SALT
We report 6 yr monitoring of a distant bright quasar CTS C30.10 (z = 0.90052)
with the Southern African Large Telescope (SALT). We measured the rest-frame
time-lag of days between the continuum variations and the response
of the Mg II emission line, using the Javelin approach. More conservative
approach, based on five different methods, imply the time delay of
days. This time delay, combined with other available
measurements of Mg II line delay, mostly for lower redshift sources, shows that
the Mg II line reverberation implies a radius-luminosity relation very similar
to the one based on a more frequently studied H line.Comment: submitted to ApJ; comments welcom
Dust reverberation mapping of the Quasar 3C273
Die vorliegende Arbeit untersucht die zentrale Struktur eines bestimmten Aktiven Galaktischen Kerns (AGN), des Quasars 3C\,273. Zu diesem Zweck wurden 5-6 Jahre optischer und Nahinfrarot-Beobachtungen ausgewertet und eine Staub-Echokartierung durchgeführt. Der gesamte beobachtete Fluss wurde in AGN, Wirtsgalaxie und Staub aufgeteilt.
Die Korrelationsanalyse zwischen der Akkretionsscheibe und dem Staubtorus zeigt eine Zeitverzögerung von 410 Tagen, die doppelt so groß ist wie bei früheren interferometrischen Studien. Zur Erklärung der Diskrepanz wird eine bestimmte zentrale Geometrie, die sogenannte "Bowl-shaped"-Geometrie, herangezogen.
Die Arbeit konzentriert sich auch auf die Implikationen dieser Ergebnisse für die weit verbreitete Staubradius-Leuchtkraft-Beziehung, für die ein neuer Wert für die Korrelation vorgeschlagen wird.
Darüber hinaus beschreibt sie die Ergebnisse der ersten photometrischen Paschen-\alpha-Echokartierung und vergleicht sie mit früheren Studien von H\beta
Time delay of Mg II emission response for the luminous quasar HE 0435-4312 : toward application of the high-accretor radius-luminosity relation in cosmology
An Absolute Calibration of the Near-infrared Period–Luminosity Relations of Type II Cepheids in the Milky Way and in the Large Magellanic Cloud
International audienceWe present time-series photometry of 21 nearby type II Cepheids in the near-infrared J , H , and K s passbands. We use this photometry, together with the Third Gaia Early Data Release parallaxes, to determine for the first time period–luminosity relations (PLRs) for type II Cepheids from field representatives of these old pulsating stars in the near-infrared regime. We found PLRs to be very narrow for BL Herculis stars, which makes them candidates for precision distance indicators. We then use archival photometry and the most accurate distance obtained from eclipsing binaries to recalibrate PLRs for type II Cepheids in the Large Magellanic Cloud (LMC). Slopes of our PLRs in the Milky Way and in the LMC differ by slightly more than 2 σ and are in a good agreement with previous studies of the LMC, Galactic bulge, and Galactic globular cluster type II Cepheids samples. We use PLRs of Milky Way type II Cepheids to measure the distance to the LMC, and we obtain a distance modulus of 18.540 ± 0.026(stat.) ± 0.034(syst.) mag in the W JK Wesenheit index. We also investigate the metallicity effect within our Milky Way sample, and we find a rather significant value of about −0.2 mag dex −1 in each band meaning that more metal-rich type II Cepheids are intrinsically brighter than their more metal-poor counterparts, in agreement with the value obtained from type II Cepheids in Galactic globular clusters. The main source of systematic error on our Milky Way PLRs calibration, and the LMC distance, is the current uncertainty of the Gaia parallax zero-point