TYC 1031-1262-1

TYC 1031-1262-1 is a spectroscopic binary in the northern constellation of Hercules, near the border with Ophiuchus, approximately 5,070 parsecs (16,500 light-years) distant. With an apparent magnitude of 11.64, it is too faint to be seen by the naked eye, but is observable using a telescope with an aperture of 60 mm (2.4 in) or larger.

The star's variability was first detected in 2005. In 2007, it was reported as the first eclipsing binary system with a type II Cepheid component to be detected in the Milky Way. It also had the shortest period of any known Cepheid binary at that time. A follow-up study in 2013, however, argues that the pulsating component is too massive to be a type II Cepheid and thus is instead an anomalous Cepheid, an object located between classical Cepheids and type II Cepheids in the Hertzsprung-Russell diagram. A similar object, NSV 10993 (V1135 Herculis), was discovered in 2008.

Physical properties The two components are both evolved bright giants (luminosity class II), more luminous than normal giant stars but less so than supergiants. The brighter of the pair (hereafter component "A") is the Cepheid that pulsates at a period of 4.15270 days, which is increasing at a rate of 2.46±0.54 min/yr for unknown reasons. It is 64% more massive than the Sun but has ballooned to 27 times the girth, radiating 764 times the luminosity of the Sun from its photosphere at an effective temperature of 5,880 K (5,610 °C; 10,120 °F), corresponding to its spectral type of F8II. Its dimmer G6II companion (B) is slightly less massive than the Sun and cooler at 4,890 K (4,620 °C; 8,340 °F), but has a radius 15 times larger and emits a little over 100 times the solar luminosity. A and B revolve around each other with an orbital period of 51.2857 days at a distance of 0.3701 AU (55,370,000 km), only twice the sum of their radii. As a result of this close proximity, the pulsation and evolution of A has been affected. Furthermore, A fills nearly 85% of its Roche lobe, while B occupies 61%, meaning that a loss or transfer of mass has likely occurred from A. The amplitude of the brightness changes caused by one star eclipsing the other is relatively small, which implies that the two stars only partially eclipse each other. The star is a member of the thick disk population, located 970 parsecs (3,200 ly) from the Galactic plane.

Nearby objects Follow-up observations on the star in 2008 revealed nine new variable stars in the immediate vicinity, including seven eclipsing binaries, one RR Lyrae variable, and one long-period, irregular or semiregular variable star.

See also V1334 Cygni: a binary system containing a classical Cepheid variable.

Footnotes

References