RU Camelopardalis

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RU Camelopardalis
RUCamLightCurve.png
A visual band light curve for RU Camelopardalis, adapted from Kollath and Szeidl (1993) [1]
Observation data
Epoch J2000       Equinox J2000
Constellation Camelopardalis
Right ascension 07h 21m 44.11647s [2]
Declination +69° 40′ 14.7192″ [2]
Apparent magnitude  (V)8.10 - 9.79 [3]
Characteristics
Spectral type C0,1-C3,2e(K0-R0) [3]
U−B color index +0.97 - +1.17 [4] (+0.9 - +1.3 [5] )
B−V color index +1.09 - +1.16 [4] (+1.0 - +1.4 [5] )
Variable type W Vir [3]
Astrometry
Radial velocity (Rv)21.20 [6]  km/s
Proper motion (μ)RA: 0.24 [2]   mas/yr
Dec.: −2.10 [2]   mas/yr
Parallax (π)0.71 ± 0.80  mas [2]
Absolute magnitude  (MV)−2.4 [7]
Details
Mass 0.57 [8]   M☉
Luminosity 417 [8]   L☉
Surface gravity (log g)1.44 [7]   cgs
Temperature 5,250 [7]   K
Metallicity [Fe/H]−0.37 [7]   dex
Other designations
RU  Cam, BD+69°417, HD  56167, HIP  35681, SAO  14157, 2MASS  J07214412+6940147, AAVSO  0710+69
Database references
SIMBAD data

RU Camelopardalis, or RU Cam, is a W Virginis variable (type II Cepheid) in the constellation of Camelopardalis. It is also a Carbon star, which is very unusual for a Cepheid variable.

Contents

History

RU Cam was reported as a new variable star in 1907. [9] It was quickly recognised as one of the Cepheid class of variable stars. [10]

The first detailed study of the spectrum of RU Cam showed that it changed during the brightness variations. From partway down the descending branch of the light curve to just after minimum brightness, the spectrum is class R with hydrogen absorption lines. The spectrum then develops hydrogen emission lines. For several days either side of maximum brightness, the spectrum becomes a relatively normal class K. [11]

RU Cam remained a somewhat unusual W Virginis variable until 1964, when the relatively regular pulsation of about 1 magnitude almost entirely stopped. [12] Since then the pulsations have varied from cycle to cycle, with amplitudes changing from several tenths of a magnitude to almost zero. [13] The light curve has a more sinusoidal shape than when it was pulsating at full amplitude and the period changes erratically between 17.4 and 26.6 days. [14]

Properties

RU Camelopardalis in optical light Ru Camelopardalis.jpg
RU Camelopardalis in optical light

RU Camelopardalis is both a Carbon star and a type II Cepheid variable star. This is unusual but not unique. At least five other relatively bright examples are known, two of which are of the BL Herculis sub-type. [15] The atmosphere contains more carbon than oxygen but is not deficient in hydrogen. This can be explained as the result of triple-alpha helium burning being processed through a CNO cycle and convected to the surface. This process occurs in some of the more massive asymptotic giant branch (AGB) stars at the third dredge-up. W Virginis stars are typically metal-poor and enriched by s-process elements, but this is not the case for RU Cam which has near-solar metallicity and no heavy metal enhancement. [7]

W Virginis variables are thought to be AGB stars executing a blue loop due to a thermal pulse from the helium burning shell. These stars cross the instability strip and undergo very regular pulsations. RU Cam fits this model reasonably well despite its peculiarities. Its temperature of around 5,000 K and luminosity several hundred times the sun's place it on or near the instability strip, and its mass about 0.6 M☉ is typical of AGB stars. [7]

The brightness variations of RU Cam are caused by pulsations which cause both the temperature and radius to vary. The temperature has been estimated to vary between 3,800 K and 5,650 K, with a change in the radius of 17 M☉ about an average size of 38 R☉. [12] Even prior to 1965, the colour variations suggested a smaller temperature range of 4,220 K - 5,240 K. [5] The maximum temperature occurs at the same time as the minimum radius, and this is when the star is near its brightest. [12]

Evolution

The evolution of a star executing a blue loop from the AGB is expected to be rapid. Period changes in RU Cam before 1965 suggest that it would cross the entire instability strip in 31,000 years. Any secular period changes since then have been masked by irregularities. [14] It is predicted that the temperature of RU Cam is increasing and it is approaching, or leaving, the bluer edge of the instability strip, in which case the pulsations would stop completely. A blueward crossing is the first crossing of the instability strip and would be followed by a second crossing when the star cools back towards the AGB. [16]

Related Research Articles

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A variable star is a star whose brightness as seen from Earth changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either:

<span class="mw-page-title-main">Chi Cygni</span> Star in the constellation Cygnus

Chi Cygni is a Mira variable star in the constellation Cygnus, and also an S-type star. It is around 500 light years away.

<span class="mw-page-title-main">RV Tauri variable</span> Class of luminous variable star

RV Tauri variables are luminous variable stars that have distinctive light variations with alternating deep and shallow minima.

<span class="mw-page-title-main">HD 84810</span> Star in the constellation Carina

HD 84810, also known as l Carinae, is a star in the southern constellation of Carina. Its apparent magnitude varies from about 3.4 to 4.1, making it readily visible to the naked eye and one of the brightest members of Carina. Based upon parallax measurements, it is approximately 1,600 light-years from Earth.

<span class="mw-page-title-main">Instability strip</span> Region of an astronomical diagram

The unqualified term instability strip usually refers to a region of the Hertzsprung–Russell diagram largely occupied by several related classes of pulsating variable stars: Delta Scuti variables, SX Phoenicis variables, and rapidly oscillating Ap stars (roAps) near the main sequence; RR Lyrae variables where it intersects the horizontal branch; and the Cepheid variables where it crosses the supergiants.

<span class="mw-page-title-main">Yellow supergiant</span> Star that has a supergiant luminosity class, with a spectral type of F or G

A yellow supergiant (YSG) is a star, generally of spectral type F or G, having a supergiant luminosity class. They are stars that have evolved away from the main sequence, expanding and becoming more luminous.

<span class="mw-page-title-main">V1401 Aquilae</span> Star in the constellation Aquila

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<span class="mw-page-title-main">TT Aquilae</span> Star in the constellation Aquila

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<span class="mw-page-title-main">Classical Cepheid variable</span>

Classical Cepheids are a type of Cepheid variable star. They are young, population I variable stars that exhibit regular radial pulsations with periods of a few days to a few weeks and visual amplitudes ranging from a few tenths of a magnitude up to about 2 magnitudes. Classical Cepheids are also known as Population I Cepheids, Type I Cepheids, and Delta Cepheid variables.

<span class="mw-page-title-main">U Camelopardalis</span> Star in the constellation Camelopardalis

U Camelopardalis is a semiregular variable star in the constellation Camelopardalis. Based on parallax measurements made by the Hipparcos spacecraft, it is located about 3,000 light-years away from the Earth. Its apparent visual magnitude is about 8, which is dim enough that it cannot be seen with the unaided eye.

<span class="mw-page-title-main">W Virginis</span> Variable star in the constellation Virgo

W Virginis is the prototype W Virginis variable, a subclass of the Cepheid variable stars. It is located in the constellation Virgo, and varies between magnitudes 9.46 and 10.75 over a period of approximately 17 days.

<span class="mw-page-title-main">Kappa Pavonis</span> Variable star in the constellation Pavo

Kappa Pavonis is a variable star in the constellation Pavo. It is the brightest W Virginis variable in the sky.

<span class="mw-page-title-main">SV Vulpeculae</span> Star in the constellation Vulpecula

SV Vulpeculae is a classical Cepheid variable star in the constellation Vulpecula. It is a supergiant at a distance of 8,700 light years.

<span class="mw-page-title-main">RT Trianguli Australis</span> Star in the constellation Triangulum Australe

RT Trianguli Australis, or RT TrA, is a BL Herculis variable in the constellation of Triangulum Australe.

<span class="mw-page-title-main">X Crucis</span> Variable star in the constellation Crux

X Crucis is a classical Cepheid variable star in the southern constellation of Crux.

<span class="mw-page-title-main">R Sagittae</span> Star in the constellation Sagitta

R Sagittae is an RV Tauri variable star in the constellation Sagitta that varies from magnitude 8.0 to 10.5 in 70.77 days. It is a post-AGB low mass yellow supergiant that varies between spectral types G0Ib and G8Ib as it pulsates. Its variable star designation of "R" indicates that it was the first star discovered to be variable in the constellation. It was discovered in 1859 by Joseph Baxendell, though classified as a semi regular variable until RV Tauri variables were identified as a distinct class in 1905.

<span class="mw-page-title-main">U Monocerotis</span> Variable star system in the constellation Monoceros

U Monocerotis is a pulsating variable star and spectroscopic binary in the constellation Monoceros. The primary star is an RV Tauri variable, a cool luminous post-AGB star evolving into a white dwarf.

<span class="mw-page-title-main">SX Centauri</span> Supergiant variable star in the constellation Centaurus

SX Centauri is a variable star in the constellation Centaurus. An RV Tauri variable, its light curve alternates between deep and shallow minima, varying its apparent magnitude from 9.1 to 12.4. From the period-luminosity relationship, it is estimated to be around 1.6 kpc from Earth. Gaia Data Release 2 gives a parallax of 0.2175 mas, corresponding to distance of about 4,600 pc.

<span class="mw-page-title-main">FG Virginis</span> Variable star in the constellation Virgo

FG Virginis is a well-studied variable star in the equatorial constellation of Virgo. It is a dim star, near the lower limit of visibility to the naked eye, with an apparent visual magnitude that ranges from 6.53 down to 6.58. The star is located at a distance of 273.5 light years from the Sun based on parallax measurements, and is drifting further away with a radial velocity of +16 km/s. Because of its position near the ecliptic, it is subject to lunar occultations.

References

  1. ↑ Kollath, Z.; Szeidl, B. (September 1993). "On the irregular light variation of RU Camelopardalis". Astronomy & Astrophysics. 277: 62–68. Bibcode:1993A&A...277...62K . Retrieved 10 November 2021.
  2. 1 2 3 4 5 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv: 0708.1752 . Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID   18759600.
  3. 1 2 3 Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-Line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  4. 1 2 Berdnikov, L. N. (2008). "VizieR Online Data Catalog: Photoelectric observations of Cepheids in UBV(RI)c (Berdnikov, 2008)". VizieR On-Line Data Catalog: II/285. Originally Published in: 2008yCat.2285....0B. 2285. Bibcode:2008yCat.2285....0B.
  5. 1 2 3 Michałowska-Smak, A.; Smak, J. (1965). "UBV Photometry of Eight Population II Cepheids". Acta Astronomica. 15: 333. Bibcode:1965AcA....15..333M.
  6. ↑ Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv: 1606.08053 . Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID   119231169.
  7. 1 2 3 4 5 6 Kipper, Tõnu; Klochkova, Valentina G. (2007). "Optical Spectroscopy of RU Cam, a Pulsating Carbon Star". Baltic Astronomy. 16: 383. arXiv: 0706.2969 . Bibcode:2007BaltA..16..383K.
  8. 1 2 Bergeat, J.; Knapik, A.; Rutily, B. (2002). "Carbon-rich giants in the HR diagram and their luminosity function". Astronomy and Astrophysics. 390 (3): 967. Bibcode:2002A&A...390..967B. doi: 10.1051/0004-6361:20020525 .
  9. ↑ Ceraski, W. (1907). "Deux nouvelles variables". Astronomische Nachrichten. 174 (5): 79–80. Bibcode:1907AN....174...79C. doi:10.1002/asna.19071740507.
  10. ↑ Shapley, H. (1918). "Studies based on the colors and magnitudes in stellar clusters. VIII. The luminosities and distances of 139 Cepheid variables". Astrophysical Journal. 48: 279. Bibcode:1918ApJ....48..279S. doi:10.1086/142435.
  11. ↑ Sanford, R. F. (1927). "On the Radial Velocity and Spectrum of the Variable Star Ru Camelopardalis". Publications of the Astronomical Society of the Pacific. 39 (230): 235. Bibcode:1927PASP...39..235S. doi:10.1086/123726. S2CID   121135072.
  12. 1 2 3 Wallerstein, George (1968). "Atmospheric Parameters for RU Cam during its Recent Quiescent Phase". Astrophysical Journal. 151: 1011. Bibcode:1968ApJ...151.1011W. doi:10.1086/149500.
  13. ↑ Broglia, P.; Conconi, P.; Guerrero, G. (1978). "The photometric behaviour of RU Cam from 1966 to 1977". Astronomy and Astrophysics. 33: 339. Bibcode:1978A&AS...33..339B.
  14. 1 2 Percy, John R.; Hale, Jonathan (1998). "Period Changes, Evolution, and Multiperiodicity in the Peculiar Population II Cepheid RU Camelopardalis". The Publications of the Astronomical Society of the Pacific. 110 (754): 1428. Bibcode:1998PASP..110.1428P. doi: 10.1086/316275 .
  15. ↑ Lloyd Evans, T. (1983). "Carbon stars among the type II Cepheids". The Observatory. 103: 276. Bibcode:1983Obs...103..276L.
  16. ↑ Zaitseva, G. V.; Lyutyi, V. M.; Efremov, Yu. N. (1973). "Cycles of Activity in RU Camelopardalis and an Evolutionary Interpretation of Its Photometric Behavior". Soviet Astronomy. 16: 856. Bibcode:1973SvA....16..856Z.
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