HM Sagittae is a dusty-type
symbiotic nova Symbiotic novae are slow irregular eruptive variable stars with very slow nova-like outbursts with an amplitude of between 9 and 11 magnitudes. The symbiotic nova remains at maximum for one or a few decades, and then declines towards its original ...
in the northern
constellation of
Sagitta.
[ It was discovered by O. D. Dokuchaeva and colleagues in 1975 when it increased in brightness by six magnitudes (a factor of around 250 brighter).][ The object displays an emission line spectrum similar to a planetary nebula and was detected in the ]radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transm ...
band in 1977.[ Unlike a classical ]nova
A nova (plural novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", which is Latin for "new") that slowly fades over weeks or months. Causes of the dramati ...
, the optical brightness of this system did not rapidly decrease with time, although it showed some variation. It displays activity in every band of the electromagnetic spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from ...
from X-ray
X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...
to radio.[
Observations in the ]infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from aroun ...
during 1978 showed this to be a very strong source with a spectrum that is consistent with a binary symbiotic system similar to V1016 Cyg. The cooler stellar component is emitting material that is then ionized by a hot component, with the emission spectrum coming from heated dust generated by the cooler star.[ By 1983, the infrared emission of the system was shown to vary by a factor of 1.5 magnitudes in the K-band with a time scale of about 500 days.][ High resolution spectral examination of the system in 1984 showed a bipolar outflow of matter with a velocity of .][ A series of knots extend outward on both sides of the central star to an angular distance of .][ The nebula surrounding the system shows a bipolar, S-shaped morphology, similar to ]R Aqr
R Aquarii (R Aqr) is a variable star in the constellation Aquarius.
R Aquarii is a symbiotic star believed to contain a white dwarf and a Mira-type variable in a binary system. The orbital period is approximately 44 years. The main Mir ...
.[
The features of the system are consistent with a central red giant star being orbited by a compact object that is accreting matter from the giant.][ The pair have an angular separation of , with the axis aligned along a position angle of . Their physical separation is estimated at .][ The giant component is most likely a Mira variable and measurements up to 1989 found a period of 527 days.][ It is surrounded by a dusty shell that is mostly composed of silicates.][ The compact object is a hot ]white dwarf
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...
with 70% of the mass of the Sun,[ which is orbited by an accretion disk. The nova-like outburst of 1975 may have been generated by a burst of mass transfer from the giant to the white dwarf during the ]periastron
An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion.
General description
There are two apsides in any el ...
passage of an eccentric orbit
In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values be ...
, leading to a thermonuclear outburst.[
Winds from both stars are colliding to produce a shock region that is a source of ]ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiati ...
emission.[ By 1985, a fading of the brightness and an increase in redness were observed, caused by dust obscuration. The hot component may be inhibiting dust formation around the giant except in the shadow region behind the star. This could explain observed individual dust obscuration events.][
]
References
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{{Stars of Sagitta
Cataclysmic variable stars
Mira variables
M-type giants
White dwarfs
Binary stars
Sagitta
Sagittae, HM