Recent Results from the High Speed Photometer

1993 ◽  
Vol 136 ◽  
pp. 356-357
Author(s):  
M. Taylor ◽  
R.C. Bless ◽  
M. Nelson ◽  
J. Percival ◽  
A. Bosh ◽  
...  
Keyword(s):  
Light Curve ◽  
White Dwarf ◽  
High Speed ◽  
Hubble Space Telescope ◽  
Hot Spot ◽  
Main Pulse ◽  
Physical Parameters ◽  
Stellar Photometry ◽  
Infrared Wavelengths ◽  
Ultraviolet Observations

AbstractOne of the first stellar photometry programs completed with the High Speed Photometer (HSP) on the Hubble Space Telescope (HST) was visual and ultraviolet observations of the Crab pulsar. We obtained continuous observations on four consecutive days using a visual filter (4000 - 7000 Å) and an additional observation, approximately two months later, using an ultraviolet filter (1600 - 3000 Å). Each observation has a time resolution of 10.7 μsec and spans approximately 30 minutes in duration. In addition to the observations made with the HSP, contemporaneous UBVR observations were also made at Jodrell Bank and McDonald Observatory. Some of the more prominent results include the following: 1) the main pulse arrival time is the same in the UV as it is in the optical and the radio regions of the spectrum, 2) there is essentially no difference in the shape of the optical pulse from one observation to the next, 3) the “flatness” of the peak of the main pulse suggests that the main pulse has been resolved in time, and 4) in accordance with the trend of observations from the radio to infrared wavelengths, the main pulse is slightly narrower in the UV than in the optical.A second HSP science observing program was a long-term program to monitor the eclipsing dwarf nova, Z Chamaeleontis (Porb = 107 minutes). We obtained a total of 42 observations of Z Cha in the UV (1120 - 1580 Å) each with a duration of approximately 45 minutes and separated by approximately three days. Although the majority of the observations cover the eclipse of the white dwarf and hot spot, a few observations were obtained outside-of-eclipse in order to obtain the complete light curve. During the course of this program, Z Cha underwent two “normal” outbursts in which the shape of the light curve changed dramatically. We will present a comparison of the light curve in quiescence with that during a “normal” outburst and quantify such geometrical and physical parameters as temperature and size of the white dwarf, hot spot, and accretion disk.

scholarly journals HST/WFC3 Complete Phase-resolved Spectroscopy of White-dwarf-brown-dwarf Binaries WD 0137 and EPIC 2122

2021 ◽  
Vol 163 (1) ◽  
pp. 17
Author(s):  
Yifan Zhou ◽  
Dániel Apai ◽  
Xianyu Tan ◽  
Joshua D. Lothringer ◽  
Ben W. P. Lew ◽  
...  
Keyword(s):  
Heat Transfer ◽  
White Dwarf ◽  
Hubble Space Telescope ◽  
Hot Spot ◽  
Brown Dwarfs ◽  
Wide Field ◽  
Brown Dwarf ◽  
Object A ◽  
M Phase ◽  
Night Flux

Abstract Brown dwarfs in close-in orbits around white dwarfs offer an excellent opportunity to investigate properties of fast-rotating, tidally locked, and highly irradiated atmospheres. We present Hubble Space Telescope Wide Field Camera 3 G141 phase-resolved observations of two brown-dwarf-white-dwarf binaries: WD 0137-349 and EPIC 212235321. Their 1.1–1.7 μm phase curves demonstrate rotational modulations with semi-amplitudes of 5.27% ± 0.02% and 29.1% ± 0.1%; both can be fit well by multi-order Fourier series models. The high-order Fourier components have the same phase as the first-order and are likely caused by hot spots located at the substellar points, suggesting inefficient day/night heat transfer. Both brown dwarfs’ phase-resolved spectra can be accurately represented by linear combinations of their respective day- and nightside spectra. Fitting the irradiated brown dwarf model grids to the dayside spectra require a filling factor of ∼50%, further supporting a hot spot dominating the dayside emission. The nightside spectrum of WD 0137-349B is fit reasonably well by non-irradiated substellar models, and the one of EPIC 21223521B can be approximated by a Planck function. We find strong spectral variations in the brown dwarfs’ day/night flux and brightness temperature contrasts, highlighting the limitations of band-integrated measurements in probing heat transfer in irradiated objects. On the color–magnitude diagram, WD 0137-349B evolves along a cloudless model track connecting the early-L and mid-T spectral types, suggesting that clouds and disequilibrium chemistry have a negligible effect on this object. A full interpretation of these high-quality phase-resolved spectra calls for new models that couple atmospheric circulation and radiative transfer under high-irradiation conditions.

scholarly journals Optical Light Curve of Nova KT Eridani

2012 ◽  
Vol 8 (S290) ◽  
pp. 191-192
Author(s):  
W. P. Chen ◽  
L. W. Hung ◽  
Fred Walter
Keyword(s):  
Light Curve ◽  
White Dwarf ◽  
Hot Spot ◽  
X Ray ◽  
Optical Emissions ◽  
Optical Light Curve ◽  
Recurrent Nova ◽  
Orbital Modulation ◽  
Type Giant

AbstractWe present the optical light curve of the very fast nova, KT Eridani, from its outburst in November 2009 to quiescence in 2012. Comparison of our data with the 24-hour monitoring by Swift on 2010 March 31 indicates a possible anticorrelation between the X-ray and optical emissions. A period of 57 d is found in the long-term optical light curve, which we interpret as the orbital modulation of the hot spot on the white dwarf disk accreting material from an early K-type giant. Our study lends support to the notation that KT Eri may be a recurrent nova.

scholarly journals Second-Order Effects due to Rotation in Pulsating Da White Dwarfs

1989 ◽  
Vol 114 ◽  
pp. 258-262
Author(s):  
P. Brassard ◽  
F. Vesemael ◽  
G. Fontaine
Keyword(s):  
Light Curve ◽  
White Dwarf ◽  
High Speed ◽  
Structural Parameters ◽  
Second Order ◽  
Order Effects ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Theoretical Predictions ◽  
Second Order Effects

The ZZ Ceti star L 19-2 is a stable pulsator whose light curve has now been deciphered with the help of over 300 hours of white light, high-speed photometry (O’Donoghue and Vamer 1982, 1987, hereafter ODV). The analysis indeed reveals the presence in the light curve of five coherent oscillations, with periods ranging from 113s to 350s. Among those, the 192s oscillation possesses three components, almost equally separated in frequency. Most importantly, the slight, but statistically significant, inequality in the frequency spacing of the triplet has been interpreted by these authors as second-order splitting of rotationally-perturbed g-mode oscillations. And indeed, the measured splitting appears consistent with the theoretical predictions of Chlebowski (1978), which are based on somewhat archaic white dwarf models. As pointed out by ODV, it is clearly of great interest to investigate 1) to what extent theoretical predictions based on more realistic, current-generation white dwarf models agree with ODVs identification, and 2) to what extent such second order effects can, eventually, be used to identify individual pulsation modes or constrain the structural parameters of variable white dwarf stars. Motivated by these questions, we have initiated a study of second-order effects due to rotation in ZZ Ceti stars, and we report here the first results of this program.

scholarly journals Z Cha – Another Case of Gravitational Radiation?

1979 ◽  
Vol 53 ◽  
pp. 503-503
Author(s):  
H. Ritter
Keyword(s):  
Gravitational Radiation ◽  
White Dwarf ◽  
Loss Rate ◽  
Main Sequence ◽  
Hot Spot ◽  
Mass Loss Rate ◽  
Physical Parameters ◽  
Low Mass ◽  
The One ◽  
R Relation

By combining spectroscopic data obtained by Vogt (1979) and photometric data obtained by Bailey (1979) and Fabian et al. (1979) it is possible to determine the physical parameters of the southern dwarf nova Z Cha (Ritter, 1979). The resulting values are: mass of the white dwarf primary M1=(0.035±0.06)M⊙, radius of the white dwarf R1=(1.8 10-2)R⊙, mass of the secondary M2=(0.16±0.02)M⊙, radius of the secondary R2=(0.19±0.01)M⊙, inclination i = 748±0.8°. Accordingly the primary conforms to the theoretical M-R relation of white dwarfs and the secondary to the theoretical low mass main sequence. The mass exchange rate derived from the luminosity of the accretion disk and from the hot spot respectively turns out to be Ṁ ≈ 4.10-11 M⊙/year, about 102 times more than is expected from the nuclear evolution of the secondary. On the other hand, angular momentum losses due to gravitational radiation predicts a mass loss rate (Faulkner, 1971) which is almost identical to the one derived from observations. Therefore after the binary pulsar (Taylor et al., 1979), Z Cha seems to be another case presenting strong evidence for the action of gravitational waves.

scholarly journals Visual Light from the Eclipsing Supersoft X-Ray Source Cal 87

1996 ◽  
Vol 158 ◽  
pp. 425-426 ◽  
Author(s):  
S. Schandl ◽  
E. Meyer-Hofmeister ◽  
F. Meyer
Keyword(s):  
Light Curve ◽  
Accretion Disk ◽  
White Dwarf ◽  
Hot Spot ◽  
Roche Lobe ◽  
X Ray ◽  
Secondary Star ◽  
The Asymmetry ◽  
The Absolute ◽  
Visual Light

We calculate the visual light curve of CAL 87 based on the assumption that an accreting, steadily burning white dwarf irradiates the accretion disk and the secondary star, as suggested by van den Heuvel et al. (1992). The shape of the eclipse light curve and the absolute luminosities put strong constraints on the contributions of the various elements in the system. We find a reasonable fit is obtained with the following sources of visual light: a Roche lobe filling secondary star where the energy from irradiation is spread out over the surface, and an accretion disk with an optically thick, cold, clumpy spray which is caused by the massive accretion stream impinging on the disk (hot spot). This spray moving around the disk and illuminated by the white dwarf is found to be the brightest source of visual light in the binary and can account for the asymmetry in the light curve.

SN2017ein: bolometric light curve and physical parameters

2017 ◽  
Vol 4 (1) ◽  
pp. 15-19
Author(s):  
P.S. Tadjimuratov ◽  
◽  
D. Mirzakulov ◽  
Keyword(s):  
Light Curve ◽  
Physical Parameters

scholarly journals An extensive photometric study of the Blazhko RR Lyrae star RZ Lyr*

2012 ◽  
Vol 423 (2) ◽  
pp. 993-1005 ◽  
Author(s):  
J. Jurcsik ◽  
Á. Sódor ◽  
G. Hajdu ◽  
B. Szeidl ◽  
Á. Dózsa ◽  
...  
Keyword(s):  
Light Curve ◽  
Light Curves ◽  
Stellar Structure ◽  
Time Base ◽  
Photometric Method ◽  
Physical Parameters ◽  
Component Solution ◽  
Rr Lyrae ◽  
Curve Variation ◽  
Type Variable

Abstract The analysis of recent, extended multicolour CCD and archive photoelectric, photographic and visual observations has revealed several important properties of RZ Lyr, an RRab-type variable exhibiting large-amplitude Blazhko modulation. On the time base of ∼110 yr, a strict anticorrelation between the pulsation- and modulation-period changes is established. The light curve of RZ Lyr shows a remarkable bump on the descending branch in the small-amplitude phase of the modulation, similarly to the light curves of bump Cepheids. We speculate that the stellar structure temporally suits a 4:1 resonance between the periods of the fundamental and one of the higher order radial modes in this modulation phase. The light-curve variation of RZ Lyr can be correctly fitted with a two-modulation-component solution; the 121-d period of the main modulation is nearly but not exactly four times longer than the period of the secondary modulation component. Using the inverse photometric method, the variations in the pulsation-averaged values of the physical parameters in different phases of both modulation components are determined.

scholarly journals New Data on the Eclipsing Binary V1848 Ori and Improved Orbital and Light Curve Solutions

2020 ◽  
Vol 29 (1) ◽  
pp. 72-80 ◽  
Author(s):  
Fatemeh Davoudi ◽  
Atila Poro ◽  
Fahri Alicavus ◽  
Afshin Halavati ◽  
Saeed Doostmohammadi ◽  
...  
Keyword(s):  
Binary System ◽  
Light Curve ◽  
Mass Function ◽  
Light Curves ◽  
Complete Analysis ◽  
Physical Parameters ◽  
Mass Ratio ◽  
Third Body ◽  
Eclipsing Binary

AbstractNew observations of the eclipsing binary system V1848 Ori were carried out using the V filter resulting in a determination of new times of minima and new ephemeris were obtained. We presented the first complete analysis of the system’s orbital period behavior and analysis of O-C diagram done by the GA and MCMC approaches in OCFit code. The O-C diagram demonstrates a sinusoidal trend in the data; this trend suggests a cyclic change caused by the LITE effect with a period of 10.57 years and an amplitude of 7.182 minutes. It appears that there is a third body with mass function of f (m3) = 0.0058 M⊙ in this binary system. The light curves were analyzed using the Wilson-Devinney code to determine some geometrical and physical parameters of the system. These results show that V1848 Ori is a contact W UMa binary system with the mass ratio of q = 0.76 and a weak fillout factor of 5.8%. The O’Connell effect was not seen in the light curve and there is no need to add spot.

VERTICAL SCALING OF TYPE I InP HBT WITH FT > 500 GHZ

2004 ◽  
Vol 14 (03) ◽  
pp. 625-631 ◽  
Author(s):  
J. W. LAI ◽  
W. HAFEZ ◽  
M. FENG
Keyword(s):  
Heterojunction Bipolar Transistors ◽  
High Speed ◽  
Impact Ionization ◽  
Cutoff Frequency ◽  
Current Gain ◽  
Vertical Scaling ◽  
Physical Parameters ◽  
Type I ◽  
Peak Current Density ◽  
Rf Performance

We have fabricated the high-speed InP/InGaAs -based single heterojunction bipolar transistors (SHBTs) with current gain cutoff frequency, fT from 166GHz to over 500GHz by the approach of vertical scaling. Collector thickness is reduced from 3000Å to 750Å and the peak current density is increased up to 1300kA/cm2. In this paper, device rf performance has been compared with respect to materials with different vertical dimensions. The scaling limitation is also studied by analytical approach. The extracted physical parameters suggest that the parasitic emitter resistance is the major limit on further enhancing ultra-scaled HBT intrinsic speed due to the associated RECBC delay. The cut-off frequency of a 500Å collector SHBT has been measured and the results indicate a dramatic drop on fT, supporting the conclusion projected by model analysis. It is also commented that for deeply downscaled HBTs, impact ionization could be another degrading mechanism limits device bandwidth.

scholarly journals A gradient field defeats the inherent repulsion between magnetic nanorods

2014 ◽  
Vol 1 (2) ◽  
pp. 140271 ◽  
Author(s):  
Yu Gu ◽  
Ruslan Burtovyy ◽  
John Custer ◽  
Igor Luzinov ◽  
Konstantin G. Kornev
Keyword(s):  
Phase Portrait ◽  
High Speed ◽  
Uniform Magnetic Field ◽  
Gradient Field ◽  
Physical Parameters ◽  
Uniform Field ◽  
Experimental Conditions ◽  
Magnetic Nanorods ◽  
Field Gradients ◽  
And Control

When controlling the assembly of magnetic nanorods and chains of magnetic nanoparticles, it is extremely challenging to bring them together side by side while keeping a desired spacing between their axes. We show that this challenge can be successfully resolved by using a non-uniform magnetic field that defeats an inherent repulsion between nanorods. Nickel nanorods were suspended in a viscous film and a non-uniform field was used to control their placement. The in-plane movement of nanorods was tracked with a high-speed camera and a detailed image analysis was conducted to quantitatively characterize the behaviour of the nanorods. The analysis focused on the behaviour of a pair of neighbour nanorods, and a corresponding dynamic model was formulated and investigated. The complex two-dimensional dynamics of a nanorod pair was analysed analytically and numerically, and a phase portrait was constructed. Using this phase portrait, we classified the nanorod behaviour and revealed the experimental conditions in which nanorods could be placed side by side. Dependence of the distance between a pair of neighbour nanorods on physical parameters was analysed. With the aid of the proposed theory, one can build different lattices and control their spacing by applying different field gradients.

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