Search Publications

Nonlinear effects associated with kinetic Alfvén wave in magnetic islands

Sharma, R. P.; Sharma, Swati; Yadav, Nitin +1 more

Observations show that kinetic Alfvén waves (KAWs) play a very important role in turbulence as well as in magnetic reconnection and have also been a topic of debate in the context of particle heating. In this paper, we aim to investigate the effect of magnetic islands on the dynamics of the nonlinear KAW. The formation of current sheet/coherent st…

High-resolution spectral analysis of unevenly spaced data using a regularization approach

Seghouani, N.

The problem of estimating the power spectrum of unevenly spaced time series is considered. Indeed, this problem is quite common in ground-based astronomy, and the use of classical methods leads to aliased frequency detection. Moreover, the spectral resolution is limited by the observation time (Shannon-Nyquist law). We propose a regularized method…

Method of frequency dependent correlations: investigating the variability of total solar irradiance

Pelt, J.; Käpylä, M. J.; Olspert, N.

Context. This paper contributes to the field of modeling and hindcasting of the total solar irradiance (TSI) based on different proxy data that extend further back in time than the TSI that is measured from satellites.
Aims: We introduce a simple method to analyze persistent frequency-dependent correlations (FDCs) between the time series and …

Luminosity Dependence of the Covering Factor of the Dust Torus in Active Galactic Nuclei Revealed by Akari

Oyabu, Shinki; Ohyama, Youichi; Takita, Satoshi +7 more

Hubble COS Spectroscopy of the Dwarf Nova CW Mon: The White Dwarf in Quiescence?

Szkody, Paula; Sion, Edward M.; Godon, Patrick +4 more

We present a synthetic spectral analysis of the HST COS spectrum of the U Geminorum-type dwarf nova CW Mon, taken during quiescence as part of our COS survey of accreting white dwarfs (WDs) in Cataclysmic Variables. We use a synthetic photosphere and optically thick accretion disk spectra to model the COS spectrum as well as archival IUE spectra o…

XMM-Newton: Status and scientific perspective

Schartel, N.; Jansen, F.; Ward, M. J.

Over the last 50 years, X-ray astronomy has become firmly established as an essential window on the universe. We review some selected scientific highlights based on observations made with XMM-Newton during the most recent few years of its 16-year operation. These range from studies of objects in our solar system to topics in cosmology. Now, as the…

Revisiting the oscillations in the cosmic microwave background angular power spectra at ℓ ∼ 120 in the Planck 2015 data

Ichiki, Kiyotomo; Horiguchi, Koichiro; Yokoyama, Jun'ichi

While the observed nearly scale-invariant initial power spectrum is regarded as favorable evidence of the standard inflationary cosmology, precision observations of the cosmic microwave background anisotropies also suggest possible existence of nontrivial features such as those observed around multipoles ℓ∼120 by WMAP. Here, we examine the Planck …

Concerning the helium-to-hydrogen number density ratio in very slow ejecta and winds near solar minimum

Farrugia, C. J.; Galvin, A. B.; Vasquez, Bernard J. +2 more

Near the solar minimum the average value of the helium-to-proton number density ratio is a strong function of speed. The average ratios for both solar ejecta and ambient winds obey approximately the same relation with speed. At the lowest speeds, the ratio takes on small values near and below 0.01. Here winds and ejecta with very slow speeds (≲310…

A Photometric Study of the Eclipsing Binary QT Ursae Majoris

Michaels, E. J.

Presented are the first multiband light curves of the eclipsing binary QT Ursae Majoris. The light curves were analyzed using the Wilson-Devinney program to find the best-fit stellar model. Asymmetries in the light curves required spots to be included in the model. The solution results give a Roche Lobe fill-out of 13%, which is consistent with a …

An analysis of magnetic reconnection events and their associated auroral enhancements

Reistad, J. P.; Milan, S. E.; Case, N. A. +2 more

An analysis of simultaneous reconnection events in the near-Earth magnetotail and enhancements in the aurora is undertaken. Exploiting magnetospheric data from the Geotail, Cluster, and Double Star missions, along with auroral images from the IMAGE and Polar missions, the relationship between a reconnection signature and its auroral counterpart is…