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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

An atlas of Doppler emission-line tomography of cataclysmic variable stars

Doppler emission-line tomography is a technique similar to medical tomography. In this atlas the emission-line profiles of cataclysmic variable stars, seen at different orbital phases, are transformed into velocity space images. This transformation makes many of the complex line profile changes easier to interpret. The emission contributions of the disk and the s-wave are clearly separated in these images, and any emission from the stream and the secondary star can often be identified. In this atlas, Doppler tomograms of Hbeta, He I lambda 4471, and He II lambda 4686 emission lines of 18 cataclysmic variable stars are presented. The Doppler images provide insights into the individual systems and a better technique for measuring and radial velocity amplitude of the white dwarf.

Kaitchuck, Ronald H.↗
NASA NTRS1997

On the Existence of Low-Luminosity Cataclysmic Variables Beyond the Orbital Period Minimum

Models of the present-day intrinsic population of cataclysmic variables predict that 99 per cent of these systems should be of short orbital period. The Galaxy is old enough that approx. 70 per cent of these stars will have already reached their orbital period minimum (approx. 80 min), and should be evolving back toward longer periods. Mass-transfer rates in these highly evolved binaries are predicted to be less or equal to 10(exp -11), leading to M(sub V) of approx. 10 or fainter, and the secondaries would be degenerate, brown dwarf-like stars. Recent observations of a group of low-luminosity dwarf novae (TOADS) provide observational evidence for systems with very low intrinsic M,. and possibly low-mass secondaries. We carry out population synthesis and evolution calculations for a range of assumed ages of the Galaxy in order to study P(sub orb) and M distributions for comparison with the TOAD observations. We speculate that at least some of the TOADs are the predicted very low- luminosity, post-period-minimum cataclysmic variables containing degenerate (brown dwarf-like) secondaries having masses between 0.02 and 0.06 M, and radii near 0.1 R., We show that these low-luminosity systems are additionally interesting in that they can be used to set a lower limit on the age of the Galaxy. The TOAD with the longest orbital period currently known (123 min), corresponds to a Galaxy age of at least 8.6 x 10(exp 9) yr.

Howell, Steve B.↗
NASA NTRS1999

Variation of Surface Air Temperature in Relation to El Nino and Cataclysmic Volcanic Eruptions, 1796-1882

During the contemporaneous interval of 1796-1882 a number of significant decreases in temperature are found in the records of Central England and Northern Ireland. These decreases appear to be related to the occurrences of El Nino and/or cataclysmic volcanic eruptions. For example, a composite of residual temperatures of the Central England dataset, centering temperatures on the yearly onsets of 20 El Nino of moderate to stronger strength, shows that, on average, the change in temperature varied by about +/- 0.3 C from normal being warmer during the boreal fall-winter leading up to the El Nino year and cooler during the spring-summer of the El Nino year. Also, the influence of El Nino on Central England temperatures appears to last about 1-2 years. Similarly, a composite of residual temperatures of the Central England dataset, centering temperatures on the month of eruption for 26 cataclysmic volcanic eruptions, shows that, on average, the change in temperature decreased by about 0.1 - 0.2 C, typically, 1-2 years after the eruption, although for specific events, like Tambora, the decrease was considerably greater. Additionally, tropical eruptions appear to produce greater changes in temperature than extratropical eruptions, and eruptions occurring in boreal spring-summer appear to produce greater changes in temperature than those occurring in fall-winter.

Wilson, Robert M.↗
NASA NTRS2008

Compositional and Geochronological Constraints on the Lunar Cataclysm from Planetary Samples

Radiometric dating and compositional clustering of lunar impact-melt rocks form the backbone of the lunar cataclysm hypothesis. Precise age determinations of Apollo and Luna impact-melt rocks define the classic formulation of the cataclysm: a large number of samples 3.9 Ga old, a steep decline after 3.9 Ga, and few impact rocks older than ~4.0 Ga. Lunar meteorites more randomly sample the lunar surface, but impact-melt clasts in these rocks show the same apparent age cutoff at 4.0 Ga (though their ages extend approx.500 Myr later). Neither do impact-formed glass spherules and fragments, formed by impacts of all sizes throughout lunar history, predate 4.0 Ga. Geological associations between compositional groups of impact-melt rocks and specific impact basins imply that five large basins formed on the Moon within 200 Myr but a counter-argument postulates they are all products of the Imbrium basin-forming impact; it is not yet proven whether groups of impact melt that are resolvable from each other in age and in trace-element composition represent multiple impacts. The 3.9 Ga age peak and subsequent steep decline are not well mirrored in meteorite data. Radiometric ages in ordinary chondrites and HED meteorites peak around 3.9 Ga but ages older and younger than 3.9 Ga are common. Among Martian meteorites, there is a single impact-related age: ALH 84001 was shocked at 3.92 Ga. Differences in relative impact velocity, impact-melt production, and sampling rate could explain differences between the meteorite and lunar records. One way to anchor the early end of the lunar flux is to directly sample the impact-melt sheet of a large lunar basin distant from Imbrium, such as the South Pole-Aitken basin, where melt rocks probably still resides on the basin floor and could be directly sampled by a human or robotic mission.

Cohen, Barbara A.↗
DOE OSTI2023

A catalogue of cataclysmic variables from 20 yr of the Sloan Digital Sky Survey with new classifications, periods, trends, and oddities

ABSTRACT We present a catalogue of 507 cataclysmic variables (CVs) observed in SDSS I to IV including 70 new classifications collated from multiple archival data sets. This represents the largest sample of CVs with high-quality and homogeneous optical spectroscopy. We have used this sample to derive unbiased space densities and period distributions for the major sub-types of CVs. We also report on some peculiar CVs, period bouncers and also CVs exhibiting large changes in accretion rates. We report 70 new CVs, 59 new periods, 178 unpublished spectra, and 262 new or updated classifications. From the SDSS spectroscopy, we also identified 18 systems incorrectly identified as CVs in the literature. We discuss the observed properties of 13 peculiar CVS, and we identify a small set of eight CVs that defy the standard classification scheme. We use this sample to investigate the distribution of different CV sub-types, and we estimate their individual space densities, as well as that of the entire CV population. The SDSS I to IV sample includes 14 period bounce CVs or candidates. We discuss the variability of CVs across the Hertzsprung–Russell diagram, highlighting selection biases of variability-based CV detection. Finally, we searched for, and found eight tertiary companions to the SDSS CVs. We anticipate that this catalogue and the extensive material included in the Supplementary Data will be useful for a range of observational population studies of CVs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Automatic Search of Cataclysmic Variables Based on LightGBM in LAMOST-DR7

The search for special and rare celestial objects has always played an important role in astronomy. Cataclysmic Variables (CVs) are special and rare binary systems with accretion disks. Most CVs are in the quiescent period, and their spectra have the emission lines of Balmer series, HeI, and HeII. A few CVs in the outburst period have the absorption lines of Balmer series. Owing to the scarcity of numbers, expanding the spectral data of CVs is of positive significance for studying the formation of accretion disks and the evolution of binary star system models. At present, the research for astronomical spectra has entered the era of Big Data. The Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST) has produced more than tens of millions of spectral data. the latest released LAMOST-DR7 includes 10.6 million low-resolution spectral data in 4926 sky regions, providing ideal data support for searching CV candidates. To process and analyze the massive amounts of spectral data, this study employed the Light Gradient Boosting Machine (LightGBM) algorithm, which is based on the ensemble tree model to automatically conduct the search in LAMOST-DR7. Finally, 225 CV candidates were found and four new CV candidates were verified by SIMBAD and published catalogs. This study also built the Gradient Boosting Decision Tree (GBDT), Adaptive Boosting (AdaBoost), and eXtreme Gradient Boosting (XGBoost) models and used Accuracy, Precision, Recall, the F1-score, and the ROC curve to compare the four models comprehensively. Experimental results showed that LightGBM is more efficient. The search for CVs based on LightGBM not only enriches the existing CV spectral library, but also provides a reference for the data mining of other rare celestial objects in massive spectral data.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2012

Characterization of New Hard X-ray Cataclysmic Variables

Aims. We aim at characterizing a sample of nine new hard X-ray selected Cataclysmic Variable (CVs), to unambiguously identify them as magnetic systems of the Intermediate Polar (IP) type. Methods. We performed detailed timing and spectral analysis by using X-ray, and simultaneous UV and optical data collected by XMM−Newton, complemented with hard X-ray data provided by INTEGRAL and Swift. The pulse arrival time were used to estimate the orbital periods. The broad band X-ray spectra were fitted using composite models consisting of different absorbing columns and emission components. Results. Strong X-ray pulses at the White Dwarf (WD) spin period are detected and found to decrease with energy. Most sources are spin-dominated systems in the X-rays, though four are beat dominated at optical wavelengths. We estimated the orbital period in all system (except for IGR J16500-3307), providing the first estimate for IGRJ08390-4833, IGRJ18308-1232, and IGR J18173-2509. All X-ray spectra are multi-temperature. V2069 Cyg and RX J0636+3535 poses a soft X-ray optically thick component at kT approx. 80 eV. An intense K (sub alpha) Fe line at 6.4 keV is detected in all sources. An absorption edge at 0.76 keV from OVII is detected in IGR J08390-4833. The WD masses and lower limits to the accretion rates are also estimated. Conclusions. We found all sources to be IPs. IGR J08390-4833, V2069 Cyg, and IGR J16500-3307 are pure disc accretors, while IGR J18308-1232, IGR J1509-6649, IGR J17195-4100, and RX J0636+3535 display a disc-overflow accretion mode. All sources show a temperature gradient in the post-shock regions and a highly absorbed emission from material located in the pre-shock flow which is also responsible for the X-ray pulsations. Reflection at the WD surface is likely the origin of the fluorescent iron line. There is an increasing evidence for the presence of a warm absorber in IPs, a feature that needs future exploration. The addition of two systems to the subgroup of soft X-ray IPs confirms a relatively large (∼ 30%) incidence.

hard X-ray↗
DOE OSTI2023

Automatic detection of cataclysmic variables from SDSS images

Abstract Investigating rare and new objects have always been an important direction in astronomy. Cataclysmic variables (CVs) are ideal and natural celestial bodies for studying the accretion process of semi-detached binaries with accretion processes. However, the sample size of CVs must increase because a lager gap exists between the observational and the theoretical expanding CVs. Astronomy has entered the big data era and can provide massive images containing CV candidates. CVs as a type of faint celestial objects, are highly challenging to be identified directly from images using automatic manners. Deep learning has rapidly developed in intelligent image processing and has been widely applied in some astronomical fields with excellent detection results. YOLOX, as the latest YOLO framework, is advantageous in detecting small and dark targets. This work proposes an improved YOLOX-based framework according to the characteristics of CVs and Sloan Digital Sky Survey (SDSS) photometric images to train and verify the model to realise CV detection. We use the Convolutional Block Attention Module to increase the number of output features with the feature extraction network and adjust the feature fusion network to obtain fused features. Accordingly, the loss function is modified. Experimental results demonstrate that the improved model produces satisfactory results, with average accuracy (mean average Precision at 0.5) of 92.0%, Precision of 92.9%, Recall of 94.3%, and $F1-score$ of 93.6% on the test set. The proposed method can efficiently achieve the identification of CVs in test samples and search for CV candidates in unlabeled images. The image data vastly outnumber the spectra in the SDSS-released data. With supplementary follow-up observations or spectra, the proposed model can help astronomers in seeking and detecting CVs in a new manner to ensure that a more extensive CV catalog can be built. The proposed model may also be applied to the detection of other kinds of celestial objects.

Astronomy & Astrophysics↗
DOE OSTI2022

A step towards unveiling the nature of three cataclysmic variables: LS Cam, V902 Mon, and SWIFT J0746.3-1608

ABSTRACT We have carried out detailed time-resolved timing analyses of three cataclysmic variables (CVs) namely LS Cam, V902 Mon, and SWIFT J0746.3-1608, using the long-baseline, high-cadence optical photometric data from the Transiting Exoplanet Survey Satellite. Our analysis of LS Cam observations hints the presence of a superorbital period of ∼4.025 ± 0.007 d along with negative and positive superhump periods of ∼3.30 and 3.70 h, respectively. These results can be explained as an interaction of nodal and apsidal precession of the accretion disc with orbital motion. For the other two sources, V902 Mon and SWIFT J0746.3-1608, we have found evidence of a beat period of 2387.0 ± 0.6 and 2409.5 ± 0.7 s, respectively, which were not found in earlier studies. Our results presented in this study indicate the change in the accretion mode during the entire observing period for both sources. For V902 Mon, an apparent orbital period derivative of (6.09 ± 0.60) × 10−10 was also found. Moreover, the second harmonic of orbital frequency dominates the power spectrum of SWIFT J0746.3-1608, suggestive of ellipsoidal modulation of the secondary star. Present analyses suggest that LS Cam could be a superhumping CV, whereas V902 Mon and SWIFT J0746.3-1608 are likely to be variable disc-overflow accreting intermediate polars.

Rawat, Nikita (ORCID:0000000246336832)↗
DOE OSTI2020

Cataclysmic Variables in the First Year of the Zwicky Transient Facility

Using selection criteria based on amplitude, time, and color, we have identified 329 objects as known or candidate cataclysmic variables (CVs) during the first year of testing and operation of the Zwicky Transient Facility. Of these, 90 are previously confirmed CVs, 218 are strong candidates based on the shape and color of their light curves obtained during 3–562 days of observation, and the remaining 21 are possible CVs but with too few data points to be listed as good candidates. Almost half of the strong candidates are within 10 deg of the galactic plane, in contrast to most other large surveys that have avoided crowded fields. The available Gaia parallaxes are consistent with sampling the low mass transfer CVs, as predicted by population models. Our follow-up spectra have confirmed Balmer/helium emission lines in 27 objects, with four showing high-excitation He ii emission, including candidates for an AM CVn, a polar, and an intermediate polar. Our results demonstrate that a complete survey of the Galactic plane is needed to accomplish an accurate determination of the number of CVs existing in the Milky Way.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Spectroscopic Studies of 30 Short-period Cataclysmic Variable Stars and Remarks on the Evolution and Population of Similar Objects

We present spectroscopy and orbital periods P {sub orb} for 30 apparently nonmagnetic cataclysmic binaries with periods below ∼3 hr, nearly all of which are dwarf novae, mostly of the SU Ursae Majoris subclass. We then turn to the evidence supporting the prediction that short-period dwarf novae evolve toward longer periods after passing through a minimum period—the “period bounce” phenomenon. Plotting data from the literature reveals that for superhump period excess ϵ = (P {sub sh} − P {sub orb})/P {sub orb} below ∼0.015, the period appears to increase with decreasing ϵ, agreeing at least qualitatively with the predicted behavior. Next, motivated by the long (decadal) outburst intervals of the WZ Sagittae subclass of short-period dwarf novae, we ask whether there could be a sizable population of “lurkers”—systems that resemble dwarf novae at minimum light, but which do not outburst over accessible timescales (or at all) and therefore do not draw attention to themselves. By examining the outburst history of the Sloan Digital Sky Survey sample of CVs, which were selected by color and not by outburst, we find that a large majority of the color-selected dwarf-nova-like objects have been observed to outburst, and we conclude that “lurkers,” if they exist, are a relatively minor part of the CV population.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Optical Studies of Eight AM Herculis–type Cataclysmic Variable Stars

We report detailed follow-up observations of eight cataclysmic variable stars (CVs) that are apparently AM Her stars, also called polars. For all, we either determine orbital periods for the first time or improve on existing determinations. The seven for which we have spectra show the high-amplitude radial-velocity curves and prominent He ii λ4686 emission lines characteristic of strongly magnetic CVs, and their periods, which range from 81 to 219 minutes, are also typical for AM Her stars. Two objects from the Gaia-alerts index, Gaia18aot and Gaia18aya, are newly identified as CVs. Another, RX J0636.3+6554, eclipses deeply, while CSS 080228:081210+040352 shows a sharp dip that is apparently a partial eclipse. The spectrum of Gaia18aya has a cyclotron harmonic near λ5500 Å that constrains the surface field to ∼49 MG or greater.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Cataclysmic Variables in the Second Year of the Zwicky Transient Facility

Using a filter in the GROWTH Marshal based on color and the amplitude and timescale of variability, we have identified 372 objects as known or candidate cataclysmic variables (CVs) during the second year of the operation of the Zwicky Transient Facility. From the available difference imaging data, we found that 93 are previously confirmed CVs and 279 are strong candidates. Spectra of four of the candidates confirm them as CVs by the presence of Balmer emission lines, while one of the four has prominent He ii lines indicative of containing a magnetic white dwarf. Gaia EDR3 parallaxes are available for 154 of these systems, resulting in distances from 108–2096 pc and absolute magnitudes in the range of 7.5–15.0, with the largest number of candidates between 10.5 and 12.5. The total numbers are 21% higher than from the previous year of the survey with a greater number of distances available but a smaller percentage of systems close to the Galactic plane. Comparison of these findings with a machine-learning method of searching all the light curves reveals large differences in each data set related to the parameters involved in the search process.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1974

Isotopic evidence for a terminal lunar cataclysm

Most highland total rock samples define a single U-Pb isochron which corresponds to a metamorphism age of about 3.9 aeons. This age is also obtained for internal U-Pb isochrons for some of these samples. The data on 18 rock samples range from concordant samples with U-238/Pb-206 ratio of about 1.2 to discordant ones with U-238/Pb-206 ratio of about 0.02. This feature, coupled with a correlated pattern of U-238/Pb-204 ratios, indicates that Pb was extensively mobilized at about 3.9 aeons. The observed Pb-U fractionation is essentially due to Pb volatilization during the metamorphic events. Volatile Pb transport is not accompanied by similar effects in Rb and must therefore be attributed to a specific process. Rb-Sr internal isochrons for the same rocks determine distinct metamorphic events in the interval 3.85 to 4.00 aeons. It is concluded that highland samples from widely separated areas bear the imprint of an event or series of events in a narrow time interval which can be identified with a cataclysmic impacting rate of the moon at about 3.9 aeons, although diffrentiation by internal magma generation cannot be excluded.

Tera, F.↗
NASA NTRS1979

2A 0526-328 - An X-ray-emitting cataclysmic variable

The weak hard X-ray source 2A 0526-328 is identified with a previously unknown cataclysmic variable on the basis of its optical emission-line spectrum and a precise X-ray location. This star has a V magnitude of about 11 and spectral properties similar to dwarf novae at minimum light and AM Her, but shows no polarization. It is likely to be a Z Camelopardalis-type system in a very extended standstill (i.e., 'novalike' or UX Ursae Majoris-type) or a recurrent nova that has not erupted in recent times.

Charles, P.↗
NASA NTRS1981

Observations of cataclysmic variables with IUE

Observations are reported of the cataclysmic variables AN UMa, 2AO311-227, VV Pup, DQ Her, and GK Per. Continuum emission was detected in the short wavelength region in DQ Her. This object exhibits a quasi-blackbody spectrum at short wavelengths, such blackbody components are a common property of the variables AM Her, SS Cyg, and U Gem, suggesting an underlying similarity in the activity of these diverse systems. Flat continuum components at longer wavelengths in general are not compatible with standard disk models. The emission line ratios in AE Aqr are anomalous in that C IV is absent to a very low level relative to N V.

Hartmann, L.↗
NASA NTRS1981

Rapid oscillations in cataclysmic variables. V - H2252-035, a single-sideband X-ray and optical pulsar

Photometric and spectroscopic observations of the optical counterpart of the X-ray source H2252-035 reveal the existence of stable periodicities of 3.59 hr and 14.31 min. Both radial velocity and photometric variations occur at the longer period, suggesting that it is the true orbital period of the underlying cataclysmic binary. The shorter period appears as a 10% modulation in the light curve, superposed on the 3.59 hr variation. The frequency is the lower orbital sideband of the X-ray pulsation frequency, suggesting that the optical pulses arise from reprocessing in the atmosphere of the secondary. Unlike the majority of X-ray pulsars, H2252-035 appears to contain a white dwarf rather than a neutron star.

Patterson, J.↗
NASA NTRS1981

Stepanian's star - The energy distribution reveals a nontypical cataclysmic variable

Einstein, IUE, optical multichannel spectrophotometry, and IR observations of Stepanian's star are discussed in terms of other known cataclysmics. While the X-ray flux and IUE emission-line data are similar to that of dwarf novae, the total continuum flux distribution from uv-IR is cooler (peaking near a 10,000 K blackbody) and is unlike either a stellar component or a classic steady-state disk. The IR data show no evidence for a late-type component.

Szkody, P.↗