Issue |
A&A
Volume 610, February 2018
|
|
---|---|---|
Article Number | A46 | |
Number of page(s) | 10 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/201730769 | |
Published online | 23 February 2018 |
A universal relation for the propeller mechanisms in magnetic rotating stars at different scales
1
INAF – Osservatorio Astronomico di Brera,
Via E. Bianchi 46,
23807
Merate,
LC, Italy
e-mail: sergio.campana@brera.inaf.it
2
INAF – Osservatorio Astronomico di Roma,
Via Frascati 33,
00078
Monteporzio Catone,
Roma, Italy
3
INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica – Milano,
Via E. Bassini 15,
20133
Milano, Italy
4
INAF – Osservatorio Astronomico di Capodimonte,
Salita Moiariello 16,
80131
Napoli, Italy
Received:
11
March
2017
Accepted:
13
November
2017
Accretion of matter onto a magnetic, rotating object can be strongly affected by the interaction with its magnetic field. This occurs in a variety of astrophysical settings involving young stellar objects, white dwarfs, and neutron stars. As matter is endowed with angular momentum, its inflow toward the star is often mediated by an accretion disc. The pressure of matter and that originating from the stellar magnetic field balance at the magnetospheric radius: at smaller distances the motion of matter is dominated by the magnetic field, and funnelling towards the magnetic poles ensues. However, if the star, and thus its magnetosphere, is fast spinning, most of the inflowing matter will be halted at the magnetospheric radius by centrifugal forces, resulting in a characteristic reduction of the accretion luminosity. The onset of this mechanism, called the propeller, has been widely adopted to interpret a distinctive knee in the decaying phase of the light curve of several transiently accreting X-ray pulsar systems. By comparing the observed luminosity at the knee for different classes of objects with the value predicted by accretion theory on the basis of the independently measured magnetic field, spin period, mass, and radius of the star, we disclose here a general relation for the onset of the propeller which spans about eight orders of magnitude in spin period and ten in magnetic moment. The parameter-dependence and normalisation constant that we determine are in agreement with basic accretion theory.
Key words: stars: neutron / X-rays: binaries / accretion, accretion discs / magnetic fields
© ESO 2018
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.