Engineering topics

Tavani, Marco

Publications and source records attributed to Tavani, Marco.

24 records · Page 2

NASA NTRS1992

Pulsar-irradiated stars in dense globular clusters

We discuss the properties of stars irradiated by millisecond pulsars in 'hard' binaries of dense globular clusters. Irradiation by a relativistic pulsar wind as in the case of the eclipsing millisecond pulsar PSR 1957+20 alter both the magnitude and color of the companion star. Some of the blue stragglers (BSs) recently discovered in dense globular clusters can be irradiated stars in binaries containing powerful millisecond pulsars. The discovery of pulsar-driven orbital modulations of BS brightness and color with periods of a few hours together with evidence for radio and/or gamma-ray emission from BS binaries would valuably contribute to the understanding of the evolution of collapsed stars in globular clusters. Pulsar-driven optical modulation of cluster stars might be the only observable effect of a new class of binary pulsars, i.e., hidden millisecond pulsars enshrouded in the evaporated material lifted off from the irradiated companion star.

Tavani, Marco↗

NASA NTRS1992

The origin of planets orbiting millisecond pulsars

A model for the formation of planets around millisecond pulsar which no longer have stellar companions is suggested. Detailed hydrodynamical models are presented which suggest that planet formation can occur either in a low-mass X-ray binary progenitor to a progenitor of a star-vaporizing millisecond pulsar when the neutron star is accreting material driven off its companion by X-ray irradiation or after a pulsar has formed and is vaporizing its companion. In both cases a circumbinary disk is created in which planets can form on a timescale of 10 exp 5 to 10 exp 6 yrs and the planets can survive a second phase in which the companion star moves toward the pulsar and is completely vaporized.

Tavani, Marco↗

NASA NTRS1992

Gamma rays from hidden millisecond pulsars

The properties were studied of a new class of gamma ray sources consisting of millisecond pulsars totally or partially surrounded by evaporating material from irradiated companion stars. Hidden millisecond pulsars offer a unique possibility to study gamma ray, optical and radio emission from vaporizing binaries. The relevance of this class of binaries for GRO observations and interpretation of COS-B data is emphasized.

Tavani, Marco↗

NASA NTRS1991

'Hidden' millisecond pulsars

The radiative and hydrodynamical processes occurring near the region where the pulsar wind interacts with the material outflowing from the illuminated companion star atmosphere are addressed. The emphasis is placed on the properties of a class of 'hidden' millisecond pulsars. Attention is given to three different classes of star-vaporizing pulsars (SVPs) characterized by a radio-emission which turns out to be sharply defined (type I), loosely defined (type II), and absent (type III), respectively. It is suggested that even though the pulsed and continuum radio emission of hidden SVPs is probably completely blocked, they can be visible in the X-ray band, gamma-ray band, and indirectly. It is shown how a class of blue stragglers might contain a rapidly spinning neutron star. Since the radiation spectrum originating from the bubble surrounding an SVP can be either relatively soft or a power-law extending up energy about 100 GeV, hidden SVPs can be important for the interpretation of X-ray and gamma-ray sources already known or to be discovered by ongoing missions such as Rosat and GRO.

Tavani, Marco↗

NASA NTRS1991

On the nature and evolution of the windy binary pulsar PSR 1744 - 24A

It is suggested that the companion of the pulsar PSR 1744 - 24A is an approximately 0.1 solar mass main-sequence star that slightly underfills its Roche lobe and is sending off a cool wind due to excitation by radiation from the pulsar. Unlike in the similarly excited system of pulsar PSR 1957 + 20, pulsar radiation pressure here almost balances wind pressure at the companion distance, leading to vastly fluctuating eclipse patterns and to occasional attempted accretion episodes that are aborted by the propeller effect and result in X-ray bursts. If this picture is correct, multiwavelength continuous observations of PSR 1744 - 24A will give valuable information about the accretion process onto neutron stars rotating with millisecond periods.

Shaham, Jacob↗

NASA NTRS1989

Self-sustained strong mass transfer without Roche lobe overflow - Cygnus X-3

It is proposed that the binary evolution of Cyg X-3 is driven by a self-excited wind from a solar composition companion star sustained by radiation from a neutron star primary. Observations would then imply that the companion is a white dwarf underfilling its Roche lobe, with mass between 0.01 and 0.03 solar masses. Cyg X-3 could then be in the late stage of very low mass X-ray binary evolution expected to result in a millisecond pulsar binary similar to the eclipsing system PSR 1957 + 20.

Tavani, Marco↗