130 research outputs found
Optical and infrared properties of V1647 Orionis during the 2003-2006 outburst. II. Temporal evolution of the eruptive source
The occurrence of new FU Orionis-like objects is fundamental to understand
the outburst mechanism in young stars and their role in star formation and disk
evolution. Our work is aimed at investigating the properties of the recent
outburst of V1647 Ori. Using optical and mid infrared long slit spectroscopy we
monitored V1647 Ori in outburst between February 2004 and January 2006. The
optical spectrum is characterized by Halpha and Hbeta in P-Cygni profile and by
many weak FeI and FeII emission lines. Short timescale variability was measured
in the continuum and line emission. On January 2006 we detected for the first
time forbidden emission lines ([OI], [SII] and [FeII]). These lines are likely
produced by an Herbig-Haro object driven by V1647 Ori. The mid infrared the
spectrum of V1647 Ori is flat and featureless at all epochs. The SED changed
drastically: the source was much redder in the early outburst than in the final
phase. The magnitude rise and the SED of V1647 Ori resembles that of a FUor
while the duration and recurrence of the outburst resemble that of a EXor. The
optical spectrum is clearly distinct from either the absorption line spectrum
of a FUor or the T Tauri-like spectrum of an EXor. Our data are consistent with
a disk instability event which led to an increase of the mass accretion rate.
The data also suggest the presence of a circumstellar envelope around the
star+disk system. The peculiar N band spectrum might be explained by dust
sublimation in the outer layers of the disk. The presence of the envelope and
the outburst statistics suggest that these instability events occur only in a
specific stage of a Class I source (e.g. in the transition phase to an
optically visible star surrounded by a protoplanetary disk). We discuss the
outburst mechanisms in term of the thermal instability model.Comment: 12 pages, 7 figures, accepted for publication in A&
Age spread in Galactic star forming region W3 Main
We present near-infrared JHKs imaging as well as K-band multi-object
spectroscopy of the massive stellar content of W3 Main using LUCI at the LBT.
We confirm 13 OB stars by their absorption line spectra in W3 Main and spectral
types between O5V and B4V have been found. Three massive Young Stellar Objects
are identified by their emission line spectra and near-infrared excess. From
our spectrophotometric analysis of the massive stars and the nature of their
surrounding HII regions we derive the evolutionary sequence of W3 Main and we
find an age spread of 2-3 Myr.Comment: 4 pages, 2 figures, To appear in conference proceedings of "370 years
of Astronomy in Utrecht
Measuring the Absolute Height and Profile of the Mesospheric Sodium Layer using a Continuous Wave Laser
We have developed and tested a novel method, based on LIDAR, of measuring the
height and profile of the mesospheric sodium layer using a continuous wave
laser. It is more efficient than classical LIDAR as the laser is on for 50% of
the time, and so can in principle be used during laser guide star adaptive
optics observations. It also has significant advantages over direct imaging
techniques because it does not require a second telescope, is almost
independent of the atmospheric conditions, and avoids triangulation problems in
determining the height. In the long term, regular monitoring using this method
would allow a valuable database of sodium layer profiles, heights, and return
flux measurements to be built up which would enable observatory staff
astronomers to schedule observations optimally. In this paper we describe the
original experiment carried out using the ALFA laser guide star system at Calar
Alto Observatory in Spain. We validate the method by comparing the LIDAR
results with those obtained from simultaneous imaging from an auxiliary
telescope. Models are presented of a similar system to be implemented in the
Very Large Telescope Laser Guide Star Facility, which will enable the initial
focus setting for the adaptive optics systems to be determined with an accuracy
of less than 200 m on a timescale of 1 minute.Comment: Accepted for publication in Astronomy & Astrophysics, 12 pages, 14
figure
LBT/LUCIFER Observations of the z~2 Lensed Galaxy J0900+2234
We present rest-frame optical images and spectra of the gravitationally
lensed, star-forming galaxy J0900+2234 (z=2.03). The observations were
performed with the newly commissioned LUCIFER1 near-infrared instrument mounted
on the Large Binocular Telescope (LBT). We fit lens models to the rest-frame
optical images and find the galaxy has an intrinsic effective radius of 7.4 kpc
with a lens magnification factor of about 5 for the A and B components. We also
discovered a new arc belonging to another lensed high-z source galaxy, which
makes this lens system a potential double Einstein ring system. Using the high
S/N rest-frame optical spectra covering H+K band, we detected Hbeta, OIII,
Halpha, NII and SII emission lines. Detailed physical properties of this high-z
galaxy were derived. The extinction towards the ionized HII regions (E_g(B-V))
is computed from the flux ratio of Halpha and Hbeta and appears to be much
higher than that towards stellar continuum (E_s(B-V)), derived from the optical
and NIR broad band photometry fitting. The metallicity was estimated using N2
and O3N2 indices. It is in the range of 1/5-1/3 solar abundance, which is much
lower than the typical z~2 star-forming galaxies. From the flux ratio of SII
6717 and 6732, we found that the electron number density of the HII regions in
the high-z galaxy were >1000 cm^-3, consistent with other z~2 galaxies but much
higher than that in local HII regions. The star-formation rate was estimated
via the Halpha luminosity, after correction for the lens magnification, to be
about 365\pm69 Msun/yr. Combining the FWHM of Halpha emission lines and the
half-light radius, we found the dynamical mass of the lensed galaxy is
5.8\pm0.9x10^10 Msun. The gas mass is 5.1\pm1.1x10^10~Msun from the H\alpha
flux surface density by using global Kennicutt-Schmidt Law, indicating a very
high gas fraction of 0.79\pm0.19 in J0900+2234.Comment: 11 pages, 6 figures accepted by ApJ, revised based on referee repor
Optical and infrared properties of V1647 Orionis during the 2003-2006 outburst. I The reflection nebula
Aims: The recent outburst of the young eruptive star V1647 Orionis has
produced a spectacular appearance of a new reflection nebula in Orion (McNeil's
nebula). We present an optical/near infrared investigation of McNeil's nebula.
This analysis is aimed at determining the morphology, temporal evolution and
nature of the nebula and its connection to the outburst.
Method: We performed multi epoch B, V, R, I, z, and K imaging of McNeil's
nebula and V1647 Ori as well as K_S imaging polarimetry. The multiband imaging
allows us to reconstruct the extinction map inside the nebula. Through
polarimetric observations we attempt to disentangle the emission from the
nebula from that of the accretion disk around V1647 Ori. We also attempt to
resolve the small spatial scale structure of the illuminating source.
Results: The energy distribution and temporal evolution of McNeil's nebula
mimic that of the illuminating source. The extinction map reveals a region of
higher extinction in the direction of V1647 Ori. Excluding foreground
extionction, the optical extinction due to McNeil's nebula in the direction of
V1647 Ori is A_V ~ 6.5 mag. The polarimetric measurement shows a compact high
polarization emission around V1647 Ori. The percentage of K_S band linear
polarization goes from 10 -- 20 %. The vectors are all well aligned with a
position angle of 90 +/- 9 degree East of North. This may correspond to the
orientation of a possible accretion disk around V1647 Ori. These findings
suggest that the appearance of McNeil's nebula is due to reflection of light by
pre-existing material in the surroundings of V1647 Ori. We also report on the
discovery of a new candidate brown dwarf or protostar in the vicinity of V1647
Ori as well as the presence of clumpy structure within HH 22A.Comment: 8 pages, 7 figures, in pres
UKIDSS detections of cool brown dwarfs - proper motions of 14 known T5 dwarfs and discovery of three new T5.5-T6 dwarfs
AIMS: We contribute to improving the census of cool brown dwarfs (late-T and
Y dwarfs) in the immediate solar neighbourhood. METHODS: By combining
near-infrared (NIR) data of UKIDSS with mid-infrared WISE and other available
NIR (2MASS) and red optical (SDSS -band) multi-epoch data we detect high
proper motion (HPM) objects with colours typical of late spectral types
(T5). We use NIR low-resolution spectroscopy for the classification of new
candidates. RESULTS: We determined new proper motions for 14 known T5.5-Y0
dwarfs, many of them being significantly (2-10 times) more accurate than
previous ones. We detected three new candidates, ULAS J0954+0623, ULAS
J1152+0359, and ULAS J1204-0150, by their HPMs and colours. Using previously
published and new UKIDSS positions of the known nearby T8 dwarf WISE J0254+0223
we improved its trigonometric parallax to 16520 mas. For the three new
objects we obtained NIR spectroscopic follow-up with LBT/LUCIFER classifying
them as T5.5 and T6 dwarfs. With their estimated spectroscopic distances of
about 25-30 pc, their proper motions of about 430-650 mas/yr lead to tangential
velocities of about 50-80 km/s typical of the Galactic thin disk population.Comment: 5 pages, 2 figures, plus 3 pages with 5 tables (online material),
accepted for publication in Astronomy and Astrophysic
Age spread in W3 Main: LBT/LUCI near-infrared spectroscopy of the massive stellar content
We present near-infrared multi-object spectroscopy and JHKs imaging of the
massive stellar content of the Galactic star-forming region W3 Main, obtained
with LUCI at the Large Binocular Telescope. We confirm 15 OB stars in W3 Main
and derive spectral types between O5V and B4V from their absorption line
spectra. Three massive Young Stellar Objects are identified by their emission
line spectra and near-infrared excess. The color-color diagram of the detected
sources allows a detailed investigation of the slope of the near-infrared
extinction law towards W3 Main. Analysis of the Hertzsprung Russell diagram
suggests that the Nishiyama extinction law fits the stellar population of W3
Main best (E(J-H)/E(H-Ks) = 1.76 and R_(Ks) = 1.44). From our
spectrophotometric analysis of the massive stars and the nature of their
surrounding HII regions we derive the evolutionary sequence of W3 Main and we
find evidence of an age spread of at least 2-3 Myr. While the most massive star
(IRS2) is already evolved, indications for high-mass pre-main-sequence
evolution is found for another star (IRS N1), deeply embedded in an ultra
compact HII region, in line with the different evolutionary phases observed in
the corresponding HII regions. We derive a stellar mass of W3 Main of (4 +- 1)
10^3 Msun, by extrapolating from the number of OB stars using a Kroupa IMF and
correcting for our spectroscopic incompleteness. We have detected the
photospheres of OB stars from the more evolved diffuse HII region to the much
younger UCHII regions, suggesting that these stars have finished their
formation and cleared away their circumstellar disks very fast. Only in the
hyper-compact HII region (IRS5), the early type stars seem to be still
surrounded by circumstellar material.Comment: Accepted by ApJ, 14 pages, 4 figure
Black Hole Mass Estimates Based on CIV are Consistent with Those Based on the Balmer Lines
Using a sample of high-redshift lensed quasars from the CASTLES project with
observed-frame ultraviolet or optical and near-infrared spectra, we have
searched for possible biases between supermassive black hole (BH) mass
estimates based on the CIV, Halpha and Hbeta broad emission lines. Our sample
is based upon that of Greene, Peng & Ludwig, expanded with new near-IR
spectroscopic observations, consistently analyzed high S/N optical spectra, and
consistent continuum luminosity estimates at 5100A. We find that BH mass
estimates based on the FWHM of CIV show a systematic offset with respect to
those obtained from the line dispersion, sigma_l, of the same emission line,
but not with those obtained from the FWHM of Halpha and Hbeta. The magnitude of
the offset depends on the treatment of the HeII and FeII emission blended with
CIV, but there is little scatter for any fixed measurement prescription. While
we otherwise find no systematic offsets between CIV and Balmer line mass
estimates, we do find that the residuals between them are strongly correlated
with the ratio of the UV and optical continuum luminosities. Removing this
dependency reduces the scatter between the UV- and optical-based BH mass
estimates by a factor of approximately 2, from roughly 0.35 to 0.18 dex. The
dispersion is smallest when comparing the CIV sigma_l mass estimate, after
removing the offset from the FWHM estimates, and either Balmer line mass
estimate. The correlation with the continuum slope is likely due to a
combination of reddening, host contamination and object-dependent SED shapes.
When we add additional heterogeneous measurements from the literature, the
results are unchanged.Comment: Accepted for publication in The Astrophysical Journal. 37 text pages
+ 8 tables + 23 figures. Updated with comments by the referee and with a
expanded discussion on literature data including new observation
Chandra and ASCA Observations of the X-ray-brightest T-Tauri Stars in the Rho Ophiuchi Cloud
We present the Chandra ACIS and ASCA GIS results for a series of four
long-term observations on DoAr 21, ROXs 21 and ROXs 31; the X-ray brightest
T-Tauri stars (TTSs) in the Rho Ophiuchi cloud. In the four observations with a
net exposure of ~600 ksec, we found six, three and two flares from DoAr 21,
ROXs 21 and ROXs 31, respectively; hence the flare rate is fairly high. The
spectra of DoAr 21 are well fitted with a single-temperature plasma model,
while those of ROXs 21 and ROXs 31 need an additional soft plasma component.
Since DoAr 21 is younger (~10^5 yr) than ROXs 21 and ROXs 31 (~10^6 yr), these
results may indicate that the soft component gradually increases as T-Tauri
stars age. The abundances are generally sub-solar and vary from element to
element. Both high-FIP (first ionization potential) and low-FIP elements show
enhancement over the mean abundances. An unusual giant flare is detected from
ROXs 31. The peak luminosity and temperature are ~10^33 ergs s^-1 and ~10 keV,
respectively. The temperature reaches its peak value before the flux maximum,
and is nearly constant (4--5 keV) during the decay phase, indicating successive
energy release during the flare. The abundances and absorption show dramatic
variability from the quiescent to flare phase.Comment: 13 pages, 18 figures, accepted for publication in Ap
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