3,238 research outputs found
HS 0139+0559, HS 0229+8016, HS 0506+7725, and HS 0642+5049 : four new long-period cataclysmic variables
We present time-resolved optical spectroscopy and photometry of four relatively bright (V ⌠14.0â15.5) long-period cataclysmic variables(CVs) discovered in the Hamburg Quasar Survey: HS 0139+0559, HS 0229+8016, HS 0506+7725, and HS 0642+5049. Their respective orbital periods, 243.69
± 0.49 min, 232.550 ± 0.049 min, 212.7 ± 0.2 min, and 225.90
± 0.23 min are determined from radial velocity and photometric variability studies. HS 0506+7725 is characterised by strong Balmer and He emission lines, short-period (âŒ10â20 min) flickering, and weak X-ray emission in the ROSAT All Sky Survey. The detection of a deep low state (B 18.5) identifies HS 0506+7725 as a member of the VY Scl
stars. HS 0139+0559, HS 0229+8016, and HS 0642+5049 display thick-disc like spectra and no or only weak flickering activity. HS 0139+0559 and HS 0229+8016 exhibit clean quasi-sinusoidal radial velocity variations of their emission lines but no or very little orbital photometricvariability. In contrast, we detect no radial velocity variation in HS 0642+5049 but a noticeable orbital brightness variation. We identify all three systems either as UX UMa-type novalike variables or as Z Cam-type dwarf novae. Our identification of these four new systems underlines that the currently known sample of CVs is rather incomplete even for bright objects. The four new systems add to the clustering of orbital periods in the 3â4 h range found in the sample of HQS selected CVs, and we discuss the large incidence of magnetic CVs and VY Scl/SW Sex stars found in this period range among the known population of CVs
The fight for accretion: discovery of intermittent mass transfer in BB Doradus in the low state
Our long-term photometric monitoring of southern nova-like cataclysmic
variables with the 1.3-m SMARTS telescope found BB Doradus fading from V ~ 14.3
towards a deep low state at V ~ 19.3 in April 2008. Here we present
time-resolved optical spectroscopy of BB Dor in this faint state in 2009. The
optical spectrum in quiescence is a composite of a hot white dwarf with Teff =
30000 +- 5000 K and a M3-4 secondary star with narrow emission lines (mainly of
the Balmer series and HeI) superposed. We associate these narrow profiles with
an origin on the donor star. Analysis of the radial velocity curve of the
H-alpha emission from the donor star allowed the measurement of an orbital
period of 0.154095 +- 0.000003 d (3.69828 +- 0.00007 h), different from all
previous estimates. We detected episodic accretion events which veiled the
spectra of both stars and radically changed the line profiles within a
timescale of tens of minutes. This shows that accretion is not completely
quenched in the low state. During these accretion episodes the line wings are
stronger and their radial velocity curve is delayed by ~ 0.2 cycle, similar to
that observed in SW Sex and AM Her stars in the high state, with respect to the
motion of the white dwarf. Two scenarios are proposed to explain the extra
emission: impact of the material on the outer edge of a cold, remnant accretion
disc, or the combined action of a moderately magnetic white dwarf (B1 <~ 5 MG)
and the magnetic activity of the donor star.Comment: 10 pages, 10 figures, accepted by MNRA
Contribution of Lianas to Plant Area Index and Canopy Structure in A Panamanian Forest
Lianas are an important component of tropical forests, where they reduce tree growth, fecundity, and survival. Competition for light from lianas may be intense; however, the amount of light that lianas intercept is poorly understood. We used a large-scale liana-removal experiment to quantify light interception by lianas in a Panamanian secondary forest. We measured the change in plant area index (PAI) and forest structure before and after cutting lianas (for 4 yr) in eight 80 m Ă 80 m plots and eight control plots (16 plots total). We used ground-based LiDAR to measure the 3-dimensional canopy structure before cutting lianas, and then annually for 2 yr afterwards. Six weeks after cutting lianas, mean plot PAI was 20% higher in control vs. liana removal plots. One yr after cutting lianas, mean plot PAI was ~17% higher in control plots. The differences between treatments diminished significantly 2 yr after liana cutting and, after 4 yr, trees had fully compensated for liana removal. Ground-based LiDAR revealed that lianas attenuated light in the upper- and middle-forest canopy layers, and not only in the upper canopy as was previously suspected. Thus, lianas compete with trees by intercepting light in the upper- and mid-canopy of this forest
AnĂĄlisis diferencial del proteoma de dos cepas de Aspergillus carbonarius con diferente nivel de producciĂłn de ocratoxina a mediante electroforesis bidimensional
Fatty acid profile and lipid composition related to spawning cycle of Queen Conch, Strombus gigas (Linnaeus), from the National Park Arrecife Alacranes, Yucatan, MĂ©xico [abstract of poster presentation]
Discovery of a Nova-Like Cataclysmic Variable in the Kepler Mission Field
We announce the identification of a new cataclysmic variable star in the
field of the Kepler Mission, KIC J192410.81+445934.9. This system was
identified during a search for compact pulsators in the Kepler field.
High-speed photometry reveals coherent large-amplitude variability with a
period of 2.94 h. Rapid, large-amplitude quasi-periodic variations are also
detected on time scales of ~1200 s and ~650 s. Time-resolved spectroscopy
covering one half photometric period shows shallow, broad Balmer and He I
absorption lines with bright emission cores as well as strong He II and Bowen
blend emission. Radial velocity variations are also observed in the Balmer and
He I emission lines that are consistent with the photometric period. We
therefore conclude that KIC J192410.81+445934.9 is a nova-like variable of the
UX UMa class in or near the period gap, and it may belong to the rapidly
growing subclass of SW Sex systems. Based on 2MASS photometry and companion
star models, we place a lower limit on the distance to the system of ~500 pc.
Due to limitations of our discovery data, additional observations including
spectroscopy and polarimetry are needed to confirm the nature of this object.
Such data will help to further understanding of the behavior of nova-like
variables in the critical period range of 3-4 h, where standard cataclysmic
variable evolutionary theory finds major problems. The presence of this system
in the Kepler mission field-of-view also presents a unique opportunity to
obtain a continuous photometric data stream of unparalleled length and
precision on a cataclysmic variable system.Comment: Accepted for publication in the Astronomical Journal. 8 pages, 7
figures, uses emulateapj
HS 0943+1404 : a true intermediate polar
We have identified a new intermediate polar, HS 0943+1404, as part of our ongoing search for cataclysmic variables in the Hamburg Quasar Survey. The orbital and white dwarf spin periods determined from time-resolved photometry and
spectroscopy are P orb 250 min and P spin = 69.171 ± 0.001 min, respectively. The combination of a large ratio P spin /P orb 0.3 and a long orbital period is very unusual compared to the other known intermediate polars. The magnetic moment of the white dwarf is estimated to be ” 1 âŒ
10 34 Gcm 3, which is in the typical range of polars. Our extensive photometry shows that HS 0943+1404 enters into deep (âŒ3 mag) low states, which are also a characteristic feature of polars. We therefore suggest that the system is a true âintermediateâ polar that will eventually synchronise, that is, a transitional object between intermediate polars and polars. The optical spectrum of HS 0943+1404 also exhibits a number of unusual emission lines, most noticeably N II λ5680, which is likely to reflect enhanced nitrogen abundances in the envelope of the secondary
Detection of the white dwarf and the secondary star in the new SU UMa dwarf nova HS 2219+1824
We report the discovery of a new, non-eclipsing SU UMa-type dwarf nova, HS 2219+1824. Photometry obtained in
quiescence (V â 17.5) reveals a double-humped light curve from which we derive an orbital period of 86.2 min. Additional photometry obtained during a superoutburst reaching V 12.0 clearly shows superhumps with a period of 89.05 min. The optical spectrum contains double-peaked Balmer and He I emission lines from the accretion disc as well as broad absorption troughs of HÎČ, HÎł, and HÎŽ from the white dwarf primary star. Modelling of the optical spectrum implies a white dwarf temperature of 13 000 K < âŒ
T eïŹ < ⌠17 000 K, a distance of 180 pc < ⌠d <
⌠230 pc, and suggests that the spectral type of the donor star is later than M 5. Phase-resolved spectroscopy obtained during quiescence reveals a narrow Hα emission line component which has a radial velocity amplitude and phase consistent with an origin on the secondary star, possibly on the irradiated hemisphere facing the white dwarf. This constitutes the first detection of line emission from the secondary star in a quiescent SU UMa star
The donor star radial velocity curve in the cataclysmic variable GY Cnc confirms white dwarf eclipse modelling mass
A large number of white dwarf and donor masses in cataclysmic variables have
been found via modelling the primary eclipse, a method that relies on untested
assumptions. Recent measurements of the mass of the white dwarf in the
cataclysmic variable GY Cnc, obtained via modelling its ultraviolet spectrum,
conflict with the mass obtained via modelling the eclipse light curve. Here we
measure the radial velocity of the absorption lines from the donor star in GY
Cnc to be kms, in excellent agreement with the
prediction based on the masses derived from modelling the eclipse light curve.
It is possible that the white dwarf mass derived from the ultraviolet spectrum
of GY Cnc is affected by the difficulty of disentangling the white dwarf
spectrum from the accretion disc spectrum.Comment: 7 pages, 6 figures, accepted for Publication in Monthly Notices of
the Royal Astronomical Societ
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