Tau1 Lupi
A B-type subgiant Beta Cephei variable in Lupus.
Tau1 Lupi, also known by its Latinized designation τ1 Lupi, is a lone star located in the southern constellation Lupus. With an apparent visual magnitude of 4.5, it can be seen without a telescope. Parallax measurements place it roughly 1,090 light-years away from the Sun. It may be a runaway star, and it belongs to the Upper Centaurus–Lupus subgroup within the nearby Sco OB2 association.
This star is a B-type subgiant with a stellar classification of B2 IV. Observations from the Cape Observatory in 1955 identified it as a Beta Cephei variable. Its brightness varies with a steady period of 0.17736934 days—equivalent to a frequency of 5.637953 cycles per day—and an amplitude of 0.035 in visual magnitude. Tau1 Lupi has about ten times the Sun’s mass and seven times its radius.
The star exhibits an infrared excess, an unusual feature for a non-emission star of its type. The inner edge of this dust lies about 980 astronomical units (AU) from the star at a temperature of 190 K, extending outward to roughly 50,000 AU where the temperature drops to 40 K. This optically thin dust is not linked to the star’s pulsations.
- Apparent visual magnitude
- 4.5
- Parallax
- 2.99 mas
- Distance
- about 1,090 light years
- Stellar classification
- B2 IV
- Variable type
- Beta Cephei
- Period
- 0.17736934 days
- Amplitude
- 0.035 in visual magnitude
Lore & Background
Tau1 Lupi is a B-type subgiant star with a stellar classification of B2 IV. Its variability was determined to be of the Beta Cephei type based on observations during 1955 at the Cape Observatory. The star shows a steady period of 0.17736934 days, corresponding to a frequency of 5.637953 cycles per day, with an amplitude of 0.035 in visual magnitude. It has around 10 times the mass of the Sun and 7 times the Sun's radius.
The star may be a runaway star, having a peculiar velocity, and is a member of the Upper Centaurus–Lupus sub-group of the nearby Sco OB2 association. Tau1 Lupi shows an infrared excess, which is unusual for a non-emission star of this class. The inner edge of the dust lies at a distance of 980 AU from the star with a temperature of 190 K, and it extends outward to as much as 50,000 AU where the temperature drops to 40 K. This optically thin dust is not related to the pulsational behavior of the star.
Reader's Guide
Tau1 Lupi holds significance as a Beta Cephei variable discovered through observations at the Cape Observatory in 1955. Its steady pulsation period of 0.17736934 days and amplitude of 0.035 in visual magnitude make it a well-characterized member of this class of variable stars. The star's membership in the Upper Centaurus–Lupus sub-group of the Sco OB2 association places it within a nearby stellar association, and its possible runaway status adds to its interest. The detection of an infrared excess around this B-type subgiant is unusual for a non-emission star, indicating the presence of a circumstellar dust disk extending from 980 AU to 50,000 AU, with temperatures ranging from 190 K to 40 K. This dust is optically thin and independent of the star's pulsational behavior, suggesting a separate evolutionary or environmental origin. Tau1 Lupi thus provides a rare example of a pulsating B star with a surrounding debris disk, offering insights into both stellar variability and circumstellar material in massive stars.
Did You Know?
- Tau1 Lupi is a solitary star in the constellation Lupus.
- It has a steady pulsation period of 0.17736934 days.
- The star shows an infrared excess unusual for a non-emission B-type star.
- Its circumstellar dust extends from 980 AU to 50,000 AU.
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