DM Ursae Majoris
First RS CVn variable classified by X-ray emission.
DM Ursae Majoris (DM UMa) is a binary star system in the northern circumpolar constellation Ursa Major. It is notable as the first RS Canum Venaticorum variable to be classified based on its X-ray emission, identified from the X-ray source 2A 1052+606 detected by the Ariel 5 satellite in 1978. The system is too faint to be seen with the naked eye, with a combined apparent visual magnitude of 9.29, and lies approximately 606 light years from the Sun.
- designations
- DM UMa, BD +61 1211, SAO 015338
- distance
- ~606 light years
- spectral_type
- K0III-IV (primary), K5V (secondary)
- orbital_period
- ~7.5 days
- variable_type
- RS Canum Venaticorum
- radial_velocity
- −7 km/s (approaching)
Lore & Background
DM UMa is a single-lined spectroscopic binary. The primary has a stellar classification of K0III-IV, and the secondary is at least 1.5 magnitudes fainter, contributing no more than 20% of the system's luminosity. The observed properties are modeled by a K0IV subgiant primary and a K5V main-sequence secondary.
Reader's Guide
DM Ursae Majoris holds significance as the first RS Canum Venaticorum variable identified through its X-ray emission, marking a milestone in linking X-ray astronomy with stellar activity. Its classification in 1979 by D. Crampton and associates demonstrated the power of X-ray surveys to uncover active binary systems. The system's extensive star spot distribution and continual H-alpha emission make it a key object for studying chromospheric activity and magnetic phenomena in close binaries. The low orbital inclination and single-lined nature provide constraints on binary evolution models. Its distance of about 606 light years and approaching radial velocity of −7 km/s place it within the context of the local stellar population. The system remains a reference for understanding RS CVn variables and their X-ray properties.
Did You Know?
- DM UMa was the first RS Canum Venaticorum variable classified based on its X-ray emission.
- The system shows continual H-alpha emission that varies by a factor of three over its orbital period.
- Its orbital period is about 7.5 days, and the system is viewed from a low inclination, nearly pole-on.
- The secondary star is at least 1.5 magnitudes fainter than the primary, contributing no more than 20% of the luminosity.
Frequently Asked Questions
What is DM Ursae Majoris?
DM UMa is a binary star system in the constellation Ursa Major, made up of a K0III-IV subgiant primary and a K5V main-sequence secondary that orbit one another with a period of roughly 7.5 days. The pair sits about 606 light years from Earth and is classified as an RS Canum Venaticorum variable.
How was DM Ursae Majoris identified as an X-ray source?
In 1978 the Ariel 5 satellite picked up an X-ray signal at the catalogue position 2A 1052+606, which was subsequently matched to this stellar pair. That association made DM UMa the first RS CVn variable whose classification was grounded in X-ray detection rather than purely optical observations.
Why is DM Ursae Majoris important to X-ray astronomy?
It holds the distinction of being the very first RS Canum Venaticorum star recognized and classified through its X-ray emission signature. That milestone helped cement X-ray brightness as a practical diagnostic for spotting magnetically active binary systems.
Can I see DM Ursae Majoris with the naked eye?
No—its combined visual magnitude of about 9.29 is far too faint for unaided vision. Even a modest backyard telescope would have difficulty resolving the two stars as a separate pair.
What are the orbital and physical characteristics of DM Ursae Majoris?
The two stars complete one mutual orbit in approximately 7.5 days, and the whole system is slowly approaching the Solar System at a radial velocity of about 7 km/s. The primary is a K0III-IV subgiant while the companion is a K5V dwarf on the main sequence.
More in Astronomical X-ray sources 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record