We present an orbit-resolved study of the magnetic cataclysmic variable (MCV) BL Hyi in its low state, and we explore the origin of its H{alpha} emission line components, their properties, and their ...possible formation mechanism. We tentatively associate one of the line components with a high-velocity component also seen in the high state. We propose a scenario in which streaming prominence-like magnetic loops (super-prominences) are kept in place by magnetic field interactions between the white dwarf and the donor star and are responsible for the high-velocity line components in the Balmer lines. We also discuss how this is in accord with the standard scenario of the secular evolution for MCVs. Finally, we offer an observational test of our ideas and present challenges for future theoretical studies.
We present new red optical spectra of V592 Cas aimed at exploring the properties of the outflow of this system in a spectral region where the underlying white dwarf and the accretion disk do not ...contribute significantly to the observed absorption components of the H alpha and He I line profiles. We use the H alpha emission line to study the wind, which appears as pronounced blueshifted P Cygni absorption troughs whose low velocity end contaminates the blue side of the emission line profile. The wind appears to be episodic in nature, with multiple events reaching velocities of 5000 km s-1 in H alpha . Similar (but weaker) wind signatures appear in the He I 5876 A line but are absent in He I 6678 A. Our data suggest that during wind episodes the wind is phase dependent and is visible for half of the orbit of the system. Considering that V592 Cas is viewed almost face-on, the symmetry axis of the outflow cannot be orthogonal to the disk and/or the outflow must have some other inherent asymmetry in outflow geometry. A possible origin of the wind is in a disk hotspot, either at the initial impact point of the accretion stream on the disk edge or as a result of disk overflow (similar to SW Sextantis stars). Simultaneous optical photometry during one night of our spectroscopic observations indicate that there is no clear relationship between the optical brightness variations and the strength of the outflow in this system.
We present two epochs of low-state, near-IR spectroscopy of the polar prototype AM Her, along with K-band spectroscopy and JHK photometry. Combining our data with long-term (RoboScope) photometry of ...the system, we determine a new spectroscopic ephemeris for AM Her. According to the new ephemeris, the primary photometric minimum of the high-state light curve of the system is centered at phase zero. Our K-band spectrum, in which the Brg and He I (2.06 mm) lines are essentially absent, confirms that during the low state, accretion was negligible. Ellipsoidal variations dominate the J-band light curve, whereas cyclotron harmonics are prominent in the H- and K-band light curves. Cyclotron emission during a time of negligible accretion has been observed in other low- polars. The Ha line is often triple peaked, and all three components follow the motion of the secondary star. The central peak likely originates from the irradiated inner hemisphere of the secondary. The blue/red satellite components reach velocities of ~300 km s-1 with respect to the secondary and coincide in phase with flaring events recently discovered from a photometric campaign. We argue that the satellite behavior is consistent with motions in large loop coronal structures on the secondary star.
A field study was conducted to determine nitrogen (N) mineralization from broiler litter (BL) in two Coastal Plain soils of
differing texture, sandy (Tifton loamy sand) or clayey (Greenville sandy ...clay loam). These soils represented the broad range
in surface textures commonly found in soils used for agricultural production in the southeastern Coastal Plain. Published
protocols used for the study were designed by the ARS mineralization team. In addition to measuring ammonium (NH 4 -N) and nitrate (NO 3 -N) in the soil as a measure of N mineralization, both total C and total N were measured to determine the impact of a single
BL amendment on C sequestration and N accumulation. Amounts of N in the soil from BL mineralization over 70 days were identical
for both soils, 46.4 mg N kg -1 soil (0.046%), but differences occurred in timing of the mineralization processes. In the sandy Tifton soil, depletion of
NH 4 -N and nitrification of the NH 4 -N to NO 3 -N occurred simultaneously. The NH 4 -N from the BL was depleted in 21 days while peak NO 3 -N concentrations in the soil were found at 28 days. In the clayey Greenville soil, NH 4 -N concentrations from BL mineralization increased for 21 days and then decreased until reaching background levels by 70 days.
Nitrate concentrations never did increase in the BL amended Greenville soil, indicating both that the nitrification rate was
much slower than the ammonification rate, and most likely, that what NO 3 -N was produced was lost from the soil by denitrification under wet conditions. The combination of soil textural and microclimate
differences along with greater protection of the BL residues in the clayey soil than in the sandy soil are believed responsible
for the observed N mineralization differences between the two soils. Previous research has shown that N mineralization rate
is positively correlated with sand content and negatively correlated with clay content of soils, and the results of this study
concurred with those findings. Measurements of total C and total N in both Coastal Plain soils showed that overall increases
were small with a single BL amendment, and it was concluded that long-term studies are needed to investigate C sequestration
and N accumulation. It was concluded from the study that there is a high probability that BL mineralization rates will be
significantly slower on the more clayey Coastal Plain soils than on very sandy ones, and that farm managers should take these
rates into consideration when planning timing and amounts of BL applications.
Analysis of 15 yr of photometric monitoring of the asynchronous magnetic cataclysmic variable BY Cam leads to revised assignments of the periodicities in the system. The surprising stability of the ...197.4-min period suggests that this is the orbital period. We confirm the 7.3-d beat period between the orbital period and the white dwarf spin period, and show that the observed periods of the orbit, spin and beat are consistent to within the errors. In earlier work, the 197.4-min period has been assigned to the 2ω−Ω sideband. Because of the observed stability of the 197.4-min period in our data, the synchronization time of BY Cam is >3500 yr (much larger than that in other asynchronous polars) if the earlier period assignments are adopted. We also suggest that ∼145-d periodicity seen in our data may be due to precession of the rotational pole of the white dwarf.
Stunted outbursts have been reported in old novae and nova‐like cataclysmic variables by Honeycutt, Robertson, and Turner. These 0.4–1 mag outbursts were concluded to be either mass transfer events ...or disk outbursts similar to dwarf nova eruptions, but seen under unusual conditions. Honeycutt, Robertson, and Turner did not have enough evidence to favor either of these possibilities. This paper uses additional long‐term photometry and analysis to argue that the similarities of these stunted outbursts to dwarf nova eruptions are now so numerous that the dwarf nova outburst choice is strongly favored. The similarities discussed here include the range of outburst spacings, the coherence and stability of the outbursts, and the presence of isolated outburst/dip pairs. As part of this discussion we note the presence of unexpectedly stable clocks over 9 years for the repetition interval of dwarf nova outbursts in SY Cnc and of stunted outbursts in FY Per.
Low-State Flaring Events in AM Herculis Kafka, S; Robertson, J; Honeycutt, R. K ...
The Astronomical journal,
05/2005, Letnik:
129, Številka:
5
Journal Article
Recenzirano
Odprti dostop
A photometric monitoring campaign has been conducted in order to investigate the character and origin of flaring events occasionally seen in the long-term low-state light curve of the polar prototype ...AM Her. Four telescopes employed during 2004 May-July revealed that the events have typical duty cycles of 2%-35%, amplitudes of 0.2-0.6 mag, and typical durations of 15-90 minutes. A striking concentration of the 2004 events appears near inferior and superior conjunction of the secondary star. Interestingly, in the long-term RoboScope-monitored light curve (1990-2003), similar events are uniformly distributed in phase. AM Her's accretion geometry and the nature of its low states allow for two likely origins for the observed events, namely, residual accretion during low states and activity (flares) on the secondary star. Considering that AM Her is likely a one-pole accretor in the low states, the former requires irregular mass transfer from the secondary, resulting in random accretion bursts, with cyclotron beaming concentrating the flares into two phase intervals. On the other hand, considering the stability of the magnetic poles, this cannot address the random distribution of the events during the long-term light curve. Drifting active regions on the secondary star could explain the random distribution of the events; however, coincidence must be invoked to explain their occurrence at the observed phases of orbital conjunction. A combination of the two ideas is also discussed, in which stellar activity on the secondary star induces random accretion bursts, with cyclotron beaming then concentrating the flares into two phase intervals.
Tracking and understanding variation in pathogens such as Batrachochytrium dendrobatidis (Bd), the agent of amphibian chytridiomycosis which has caused population declines globally, is a priority for ...many land managers. However, relatively little sampling of amphibian communities has occurred at high latitudes. We used skin swabs collected during 2005-2017 from boreal toads Anaxyrus boreas (n = 248), in southeast Alaska (USA; primarily in and near Klondike Gold Rush National Historical Park KLGO) and northwest British Columbia (Canada) to determine how Bd prevalence varied across life stages, habitat characteristics, local species richness, and time. Across all years, Bd prevalence peaked in June and was >3 times greater for adult toads (37.5%) vs. juveniles and metamorphs (11.2%). Bd prevalence for toads in the KLGO area, where other amphibian species are rare or absent, was highest from river habitats (55.0%), followed by human-modified upland wetlands (32.3%) and natural upland wetlands (12.7%)-the same rank-order these habitats are used for toad breeding. None of the 12 Columbia spotted frogs Rana luteiventris or 2 wood frogs R. sylvatica from the study area tested Bd-positive, although all were from an area of low host density where Bd has not been detected. Prevalence of Bd on toads in the KLGO area decreased during 2005-2015. This trend from a largely single-species system may be encouraging or concerning, depending on how Bd is affecting vital rates, and emphasizes the need to understand effects of pathogens before translating disease prevalence into management actions.
Projected increases in wildfire and other climate-driven disturbances will affect populations and communities worldwide, including host-parasite relationships. Research in temperate forests has shown ...that wildfire can negatively affect amphibians, but this research has occurred primarily outside of managed landscapes where interactions with human disturbances could result in additive or synergistic effects. Furthermore, parasites represent a large component of biodiversity and can affect host fitness and population dynamics, yet they are rarely included in studies of how vertebrate hosts respond to disturbance. To determine how wildfire affects amphibians and their parasites, and whether effects differ between protected and managed landscapes, we compared abundance of two amphibians and two nematodes relative to wildfire extent and severity around wetlands in neighboring protected and managed forests (Montana, USA). Population sizes of adult, male long-toed salamanders (
Ambystoma macrodactylum
) decreased with increased burn severity, with stronger negative effects on isolated populations and in managed forests. In contrast, breeding population sizes of Columbia spotted frogs (
Rana luteiventris
) increased with burn extent in both protected and managed protected forests. Path analysis showed that the effects of wildfire on the two species of nematodes were consistent with differences in their life history and transmission strategies and the responses of their hosts. Burn severity indirectly reduced abundance of soil-transmitted
Cosmocercoides variabilis
through reductions in salamander abundance. Burn severity also directly reduced
C. variabilis
abundance, possibly though changes in soil conditions. For the aquatically transmitted nematode
Gyrinicola batrachiensis
, the positive effect of burn extent on density of Columbia spotted frog larvae indirectly increased parasite abundance. Our results show that effects of wildfire on amphibians depend upon burn extent and severity, isolation, and prior land use. Through subsequent effects on the parasites, our results also reveal how changes in disturbance regimes can affect communities across trophic levels.
We present observations in the red region of the spectrum of the magnetic cataclysmic variable prototype AM Her during its 2005 low state. We confirm the unexpected structure of the Ha emission line ...and verify most of the conclusions of our earlier study: the line is typically triple-peaked, and the radial velocity curves of all three components are phased with the radial velocities of absorption features from the photosphere of the M dwarf secondary star. The red and blue satellites of the central Ha peak were interpreted in the earlier paper as arising from magnetically confined gas motions in large, long-lived loop prominences on the secondary star; our new data are consistent with that conclusion. Furthermore, although the radial velocities of the strong central peak of the Ha emission line suggested an origin from the irradiation-heated inner hemisphere of the secondary, the phase variation of the equivalent width of the line in these new data is inconsistent with such an interpretation. It is likely that the central component of Ha has a significant contribution from stellar activity on the secondary star. Finally, simultaneous V-band photometry of the system was acquired during much of the spectroscopy, with the expectation that the ~0.6 mag flares seen in earlier data might be correlated with changes in Ha. Although the strength of Ha increased by ~1.5 times on several brief occasions during the spectroscopy, no simultaneous photometric flaring was detected.
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