85 research outputs found
Photometric study of selected cataclysmic variables II. Time-series photometry of nine systems
We present time-series photometry of nine cataclysmic variables: EI UMa,
V844Her, V751 Cyg, V516 Cyg, GZ Cnc, TY Psc, V1315 Aql, ASAS J002511+1217.12,
V1315 Aql and LN UMa. The observations were conducted at various observatories,
covering 170 hours and comprising 7,850 data points in total.
For the majority of targets we confirm previously reported periodicities and
for some of them we give, for the first time, their spectroscopic orbital
periods. For those dwarf-nova systems which we observed during both quiescence
and outburst, the increase in brightness was followed by a decrease in the
amount of flickering. Quasi-periodic oscillations have either been discovered,
or were confirmed. For the eclipsing system V1315 Aql we have covered 9
eclipses, and obtained a refined orbital ephemeris. We find that, during its
long baseline of observations, no change in the orbital period of this system
has occurred. V1315 Aql also shows eclipses of variable depth.Comment: 30 pages, 16 figures, 4 tables. Submitted to JA
Modelling the structure and kinematics of the Firework nebula: The nature of the GK Persei nova shell and its jet-like feature
Aims. The shaping mechanisms of old nova remnants are probes for several important and unexplained processes, such as dust formation and the structure of evolved star nebulae. To gain a more complete understanding of the dynamics of the GK Per (1901) remnant, an examination of symmetry of the nova shell is explored, followed by a kinematical analysis of the previously detected jet-like feature in the context of the surrounding fossil planetary nebula.
Methods. Faint-object high-resolution echelle spectroscopic observations and imaging were undertaken covering the knots which comprise the nova shell and the surrounding nebulosity. New imaging from the Aristarchos telescope in Greece and long-slit spectra from the Manchester Echelle Spectrometer instrument at the San Pedro Martir observatory in Mexico were obtained, supplemented with archival observations from several other optical telescopes. Position-velocity arrays are produced of the shell, and also individual knots, and are then used for morpho-kinematic modelling with the shape code. The overall structure of the old knotty nova shell of GK Per and the planetary nebula in which it is embedded is then analysed.
Results. Evidence is found for the interaction of knots with each other and with a wind component, most likely the periodic fast wind emanating from the central binary system. We find that a cylindrical shell with a lower velocity polar structure gives the best model fit to the spectroscopy and imaging. We show in this work that the previously seen jet-like feature is of low velocity.
Conclusions. The individual knots have irregular tail shapes; we propose here that they emanate from episodic winds from ongoing dwarf nova outbursts by the central system. The nova shell is cylindrical, not spherical, and the symmetry axis relates to the inclination of the central binary system. Furthermore, the cylinder axis is aligned with the long axis of the bipolar planetary nebula in which it is embedded. Thus, the central binary system is responsible for the bipolarity of the planetary nebula and the cylindrical nova shell. The gradual planetary nebula ejecta versus sudden nova ejecta is the reason for the different degrees of bipolarity. We propose that the “jet” feature is an illuminated lobe of the fossil planetary nebula that surrounds the nova shell
A long trail behind the planetary nebula HFG1 (PK 136+05) and its precataclysmic binary central star V664 Cas
A deep wide-field image in the light of the Halpha+[N II] emission lines, of
the planetary nebula HFG1 which surrounds the precataclysmic binary system V664
Cas, has revealed a tail of emission at least 20' long, at a position angle of
316deg. Evidence is presented which suggests that this is an ~10^5 y old trail
of shocked material, left behind V664 Cas as it ejects matter whilst ploughing
through its local interstellar media at anywhere between 29 and 59 km/s
depending on its distance from the Sun.Comment: 3 pages, 1 figure, accepted for publication in MNRA
Discovery of an optical cocoon tail behind the runaway HD 185806
Studies on the circumstellar structures around evolved stars provide vital
information on the evolution of the parent star and the properties of the local
interstellar medium. In this work, we present the discovery and
characterization of an optical cocoon tail behind the star HD 185806. The
cocoon apex emission is puzzling, as it is detected in the infrared but shows
no signal in the optical wavelength. The H-alpha and [OIII] fluxes of the
nebular structure vary from 2.7 to 8.5x10^{-12} erg s^{-1} cm^ {-2} and from
0.9 to 7.0x10^{-13} erg s^{-1} cm^{-2}, respectively. Through high-resolution
spectroscopy, we derive the spectral type of the star, construct the
position-velocity diagrams of the cocoon tail for the H-alpha, [OIII] and [NII]
emission lines, and determine its velocity in the range of -100 to 40 km s
^{-1} . Furthermore, we use SED fitting and MESA evolutionary models adopting a
distance of 900 pc, and classify HD 185806 as a 1.3 M star, in the transition
phase between the RGB and early AGB stages. Finally, we study the
morpho-kinematic structure of the cocoon tail using the astronomical software
SHAPE. An ellipsoidal structure, with an inclination of 19 degrees with respect
to the plane of sky is found to better reproduce the observed cocoon tail of HD
185806.Comment: Accepted 2022 June 29. Received 2022 June 24; in original form 2022
May 26, 14 pages. Dedicated to V.G. who passed away on 2 Sept. 202
Two New Nova Shells associated with V4362 Sagittarii and DO Aquilae
A classical nova is an eruption on the surface of a white dwarf in an accreting binary system. The material ejected from the white dwarf surface generally forms an axisymmetric shell. The shaping mechanisms of nova shells are probes of the processes that take place at energy scales between planetary nebulae and supernova remnants. We report on the discovery of nova shells surrounding the post-nova systems V4362 Sagittarii (1994) and more limited observations of DO Aquilae (1925). Distance measurements of 0.5p/m1.4 kpc for V4362 Sgr and 6.7 p/m 3.5 kpc -0.2 for DO Aql are found based on the expansion parallax method. The growth rates are measured to be 0.07``/year for DO Aql and 0.32``/year for V4362 Sgr. A preliminary investigation into the ionisation structure of the nova shell associated with V4362 Sgr is presented. The observed ionisation structure of nova shells depends strongly on their morphology and the orientation of the central component towards the observer. X-ray, IR and UV observations as well as optical integral field unit spectroscopy are required to better understand these interesting objects
Detection of optical emission from the supernova remnant G7.7–3.7
The work of VD is supported by a grant from NWO graduate programme/GRAPPA-PhD programme. VD also acknowledges support from the LKBF, subsidy no. 19.2.027. JVHS acknowledges support from STFC grant ST/R000824/1. PZ acknowledges the support from the NWO Veni Fellowship, grant no. 639.041.647 and NSFC grant 11590781. SA thanks the support under the grant 5077 financed by IAASARS/NOA. AdB thanks the support from the Spanish Government Ministerio de Ciencia e Innovación through grants PGC-2018-091, 3741-B-C22, and SEV 2015-0548, from the Canarian Agency for Research, Innovation and Information Society (ACIISI) of the Canary Islands Government, and from the European Regional Development Fund (ERDF), under grant with reference ProID2017010115.We present the first optical study of the supernova remnant (SNR) G7.7–3.7, with the aim of determining its evolutionary phase since it has been suggested to be the remnant of SN 386 AD. We obtained narrow-band images in the filters H α + [N ii], H β, [O iii], [S ii] that revealed faint optical emission in the southern region of the SNR consisting of two filaments elongated in the east–west direction aligned with the X-ray emitting region of the remnant. The filaments were seen in H α + [N ii], [O iii] images and marginally in the [S ii] images, with a non-detection in H β. Long-slit spectroscopy of the three regions along one filament revealed large ratios of [S ii]/H α = (1.6–2.5), consistent with that expected for a shock-heated SNR. The [S ii] doublet ratio observed in two of the regions implies an upper limit for the electron density of the gas, with estimates falling below 400 cm−3 and 600 cm−3 in the respective areas. We discuss potential physical mechanisms that formed the observed optical filaments and we suggest that most likely they resulted by a collision of the SNR with a dense circumstellar shell lying at the southern region of the remnant.Publisher PDFPeer reviewe
Detection of optical emission from the supernova remnant G7.7-3.7
We present the first optical study of the supernova remnant (SNR) G7.7-3.7,
with the aim of determining its evolutionary phase since it has been suggested
to be the remnant of SN 386 AD. We obtained narrow-band images in the filters
H + [NII], H, [OIII], [SII] that revealed faint optical emission
in the southern region of the SNR consisting of two filaments elongated in the
east-west direction aligned with the X-ray emitting region of the remnant. The
filaments were seen in H + [NII], [OIII] images and marginally in the
[SII] images, with a non-detection in H. Long-slit spectroscopy of three
regions along one filament revealed large ratios of [SII] / H =
(1.6-2.5), consistent with that expected for a shock-heated SNR. The [SII]
doublet ratio observed in two of the regions implies an upper limit for the
electron density of the gas, with estimates falling below 400 cm and 600
cm in the respective areas. We discuss potential physical mechanisms
that formed the observed optical filaments and we suggest that most likely they
resulted by a collision of the SNR with a dense circumstellar shell lying at
the southern region of the remnant.Comment: 10 pages, 5 figures, accepted in MNRA
Photometric study of selected cataclysmic variables
We present time-resolved photometry of five relatively poorly-studied
cataclysmic variables: V1193 Ori, LQ Peg, LD 317, V795 Her, and MCT 2347-3144.
The observations were made using four 1m-class telescopes for a total of more
than 250 h of observation and almost 16,000 data points. For LQ Peg WHT
spectroscopic data have been analysed as well.
The light curves show a wide range of variability on different time scales
from minutes to months. We detect for the first time a brightness variation of
0.05 mag in amplitude in V1193 Ori on the same timescale as the orbital period,
which we interpret as the result of the irradiation of the secondary. A 20-min
quasi-periodic oscillation is also detected. The mean brightness of the system
has changed by 0.5 mag on a three-month interval, while the flickering was
halved. In LQ Peg a 0.05 mag modulation was revealed with a period of about 3
h. The flickering was much smaller, of the order of 0.025 mag. A possible
quasi-periodic oscillation could exist near 30 min. For this object, the WHT
spectra are single-peaked and do not show any radial-velocity variations. The
data of LD 317 show a decrease in the mean magnitude of the system. No periodic
signal was detected but this is certainly attributable to the very large
flickering observed: between 0.07 and 0.1 mag. For V795 Her, the 2.8-hour
modulation, thought to be a superhump arising from the precession of the disc,
is present. We show that this modulation is not stable in terms of periodicity,
amplitude, and phase. Finally, for MCT 2347-3144, a clear modulation is seen in
a first dataset obtained in October 2002. This modulation is absent in August
2003, when the system was brighter and showed much more flickering.Comment: 19 pages, 15 figures, 7 tables. Accepted for pubication by A&
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