22 research outputs found
New powerful outburst of the unusual young star V1318 Cyg S (LkH{\alpha} 225)
Young double star V1318 Cyg, which is associated with a small isolated
star-forming region around HAeBe star BD+40o4124, has very unusual photometric
and spectral behavior. We present results of photometric and spectroscopic
observations in the optical range. We carried out BVRI CCD photometric
observations of V1318 Cyg from 2015 Sept. to 2017 July. For the same period we
acquired medium- and low-resolution spectra. Observations were performed with
the 2.6 m telescope. We analyze the historical light curve for V1318 Cyg and
demonstrate that the southern component, V1318 Cyg S, after being rather bright
in the 1970s (V14 mag) started to lower its brightness and in 1990
became practically invisible in the optical. After its reappearance in the
second half of the 1990s the star started to become very slowly brighter.
Between 2006 and 2010 V1318 Cyg S started brightening more quickly, and in 2015
had become brighter by more than five magnitudes in visible light. Since this
time V1318 Cyg S has remained at this maximum. Its spectrum shows little
variability and consists of a mixture of emission and absorption lines, which
has allowed for estimates of its spectral type as early Ae, with obvious
evidence of matter outflow. We derive its current A(V) 7.2 and L = 750
L(sun) thus confirming that V1318 Cyg S should belong to the Herbig Ae stars,
making it, along with BD+40o4124 and V1686 Cyg, the third luminous young star
in the group. It is very probable that we observe V1318 Cyg S near the pole and
that the inclination of its dense and slow ( 100 km/s) outflow is low.
The unusual variability and other features of V1318 Cyg S make it difficult to
classify this star among known types of eruptive young stars. It could be an
extreme, higher-mass example of an EXor, or an object of intermediate class
between EXors and FUors, like V1647 Ori.Comment: 9 pages, 7 figure
Two epoch spectro-imagery of FS Tau B outflow system
Herbig-Haro (HH) flows exhibit a large variety of morphological and
kinematical structures such as bow shocks, Mach disks, and deflection shocks.
Both proper motion (PM) and radial velocity investigations are essential to
understand the physical nature of such structures. We investigate the
kinematics and PM of spectrally separated structures in the FS~Tau~B HH flow.
Collating these data makes it possible to understand the origin of these
structures and to explain the unusual behavior of the jet. On the other hand,
the study of emission profiles in the associated reflection nebulae allows us
to consider the source of the outflow both from edge-on and pole-on points of
view. We present the observational results obtained with the 6 m telescope at
the Special Astrophysical Observatory of the Russian Academy of Sciences using
the SCORPIO multimode focal reducer with a scanning Fabry-Perot interferometer.
Two epochs of the observations of the FS~Tau~B region in H emission
(2001 and 2012) allowed us to measure the PM of the spectrally separated inner
structures of the jet. In addition to already known emission structures in the
FS~Tau~B system, we discover new features in the extended part of the jet and
in the counter-jet. Moreover, we reveal a new HH knot in the HH~276 independent
outflow system and point out its presumable source. In the terminal working
surface of the jet, structures with different radial velocities have PMs of the
same value. This result can be interpreted as the direct observation of
bow-shock and Mach disk regions. A bar-like structure, located southwest from
the source demonstrates zero PM and can be considered as one more example of
deflection shock. An analysis of H profiles in the reflection nebulae
R1 and R3 indicates the uniqueness of this object, which can be studied in
pole-on and edge-on directions simultaneously.Comment: 8 pages, 11 figure
Proper motions of spectrally selected structures in the HH 83 outflow
We continue our program of investigation of the proper motions of spectrally
separated structures in the Herbig-Haro outflows with the aid of Fabry-Perot
scanning interferometry. This work mainly focuses on the physical nature of
various structures in the jets. The aim of the present study is to measure the
proper motions of the previously discovered kinematically separated structures
in the working surface of the HH 83 collimated outflow. We used observations
from two epochs separated by 15 years, which were performed on the 6m telescope
with Fabry-Perot scanning interferometer. We obtained images corresponding to
different radial velocities for the two separate epochs, and used them to
measure proper motions. In the course of our data analysis, we discovered a
counter bow-shock of HH 83 flow with positive radial velocity, which makes this
flow a relatively symmetric bipolar system. The second epoch observations
confirm that the working surface of the flow is split into two structures with
an exceptionally large (250 km\ s) difference in radial velocity. The
proper motions of these structures are almost equal, which suggests that they
are physically connected. The asymmetry of the bow shock and the turning of
proper motion vectors suggests a collision between the outflow and a dense
cloud. The profile of the H line for the directly invisible infrared
source HH 83 IRS, obtained by integration of the data within the reflection
nebula, suggests it to be of P Cyg type with a broad absorption component
characteristic of the FU Ori like objects. If this object underwent an FU Ori
type outburst, which created the HH 83 working surfaces, its eruption took
place about 1500 years ago according to the kinematical age of the outflow.Comment: 7 pages, 6 figure
Kinematics and the origin of the internal structures in HL Tau jet (HH 151)
Knotty structures of Herbig-Haro jets are common phenomena, and knowing the
origin of these structures is essential for understanding the processes of jet
formation. Basically, there are two theoretical approaches: different types of
instabilities in stationary flow, and velocity variations in the flow. We
investigate the structures with different radial velocities in the knots of the
HL Tau jet as well as its unusual behaviour starting from 20 arcsec from the
source. Collation of radial velocity data with proper motion measurements of
emission structures in the jet of HL Tau makes it possible to understand the
origin of these structures and decide on the mechanism for the formation of the
knotty structures in Herbig-Haro flows. We present observations obtained with a
6 m telescope (Russia) using the SCORPIO camera with scanning Fabry-Perot
interferometer. Two epochs of the observations of the HL/XZ Tau region in
Halpha emission (2001 and 2007) allowed us to measure proper motions for high
and low radial velocity structures. The structures with low and high radial
velocities in the HL Tau jet show the same proper motion. The point where the
HL Tau jet bents to the north (it coincides with the trailing edge of so-called
knot A) is stationary, i.e. does not have any perceptible proper motion and is
visible in Halpha emission only. We conclude that the high- and low- velocity
structures in the HL Tau jet represent bow-shocks and Mach disks in the
internal working surfaces of episodic outflows. The bend of the jet and the
brightness increase starting some distance from the source coincides with the
observed stationary deflecting shock. The increase of relative surface
brightness of bow-shocks could be the result of the abrupt change of the
physical conditions of the ambient medium as well as the interaction of a
highly collimated flow and the side wind from XZ Tau.Comment: To be published in Astronomy and Astrophysic
Inner disc rearrangement revealed by dramatic brightness variations in the young star PV Cep
Young Sun-like stars at the beginning of the pre-main sequence (PMS)
evolution are surrounded by accretion discs and remnant protostellar envelopes.
Photometric and spectroscopic variations of these stars are driven by
interactions of the star with the disc. Time scales and wavelength dependence
of the variability carry information on the physical mechanisms behind these
interactions. We conducted multi-epoch, multi-wavelength study of PV Cep, a
strongly variable, accreting PMS star. By combining our own observations from
2004-2010 with archival and literature data, we show that PV Cep started a
spectacular fading in 2005, reaching an I_C-band amplitude of 4 mag. Analysis
of variation of the optical and infrared fluxes, colour indices, and emission
line fluxes suggests that the photometric decline in 2005-2009 resulted from an
interplay between variable accretion and circumstellar extinction: since the
central luminosity of the system is dominated by accretion, a modest drop in
the accretion rate could induce the drastic restructuring of the inner disc.
Dust condensation in the inner disc region might have resulted in the
enhancement of the circumstellar extinction.Comment: 11 pages, 4 figures, accepted for publication by MNRAS. 3 online
tables adde
Magnetospheric accretion-ejection processes in the classical T Tauri star AA
From a long time series of high resolution (R=115,000) HARPS spectra and
simultaneous broad-band photometry, we report new evidence for magnetospheric
accretion as well as ejection processes in the nearly edge-on classical T Tauri
star AA Tau.
AA Tau's light curve is modulated with a period of 8.22d. The recurrent
luminosity dips are due to the periodic occultation of the central star by the
magnetically-warped inner disk edge located at about 9 Rstar. Balmer line
profiles exhibit a clear rotational modulation of high-velocity redshifted
absorption components with a period of 8.22 days as well, with a maximum
strength when the main accretion funnel flow passes through the line of sight.
At the same time, the luminosity of the system decreases by about 1 mag,
indicative of circumstellar absorption of the stellar photosphere by the
magnetically-warped, corotating inner disk edge. The photospheric and HeI
radial velocities also exhibit periodic variations, and the veiling is
modulated by the appearance of the accretion shock at the bottom of the
accretion funnel. Diagnostics of hot winds and their temporal behaviour are
also presented.
The peculiar geometry of the young AA Tau system (nearly edge-on) allows us
to uniquely probe the acretion-ejection region close to the star. We find that
most spectral and photometric diagnostics vary as expected from models of
magnetically-channelled accretion in young stars, with a large scale
magnetosphere tilted by 20 deg onto the star's spin axis. We also find evidence
for time variability of the magnetospheric accretion flow on a timescale of a
few rotational periods.Comment: 14 page