DY Persei

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DY Persei
Tr 2.png
Red circle.svg
Location of DY Persei (circled) near Trumpler 2 (Stellarium-generated image)
Observation data
Epoch J2000.0       Equinox J2000.0
Constellation Perseus
Right ascension 02h 35m 17.127s [1]
Declination +56° 08 44.72 [1]
Apparent magnitude  (V)10.5 - 16.0 [2]
Characteristics
Spectral type C5,4pJ: [3] C-R4+ C25.5 [4]
B−V color index 1.79 [5]
V−R color index 1.12 [5]
J−H color index 0.185 [6]
J−K color index 1.963 [6]
Variable type DY Per [7]
Astrometry
Radial velocity (Rv)−38 [8]  km/s
Proper motion (μ)RA: +2.264 [1]   mas/yr
Dec.: −0.675 [1]   mas/yr
Parallax (π)0.6718 ± 0.0251  mas [1]
Distance 1,500 [9]   pc
Absolute magnitude  (MV)2.5 (max) [7]
Details
Radius 87 [10]   R
Luminosity 522 [11]   L
Surface gravity (log g)0.0 [12]   cgs
Temperature 2,900-3,100 [12]   K
Metallicity [Fe/H]2.0 to 0.5 [12]   dex
Other designations
DY  Persei, DY  Per, 2MASS  J02351713+5608446, AAVSO  0228+55, IRAS  02316+5555, TYC 3691-1782-1
Database references
SIMBAD data

DY Persei is a variable star and carbon star in the Perseus constellation. At maximum it is 11th magnitude and at its faintest it drops to 16th magnitude. DY Persei is the prototype of the very rare DY Persei class of variables that pulsate like red variables but also fade from sight like R Coronae Borealis variables.

Contents

Location

DY Persei is located on the outskirts of the Trumpler 2 open cluster, near the famous Double Cluster. At 1,500 pc, DY Persei is thought to be much further away than Trumpler 2 and not a member.

Variability

Light curve of DY Persei from 2014 to 2017, showing pulsations interrupted by a deep decline DY Persei.png
Light curve of DY Persei from 2014 to 2017, showing pulsations interrupted by a deep decline

DY Persei was reported to be variable in 1947. [13] It was initially classified as a semiregular variable star with a brightness range of magnitude 10.6 to 13.2 and an approximate period of 900 days. [14] Further study revealed that it showed deep declines every few years as well as continuous variations with a rough period of 792 days. The deep declines were considered to be related to the declines seen in R CrB stars, but DY Persei was a unique example, being a cool carbon star and showing large amplitude semiregular variations when not in decline. [15]

DY Persei is now classed as a member of the very rare class of DY Persei variables, with only four known in the Milky Way and 13 more in the Magellanic Clouds. [16] It has shown declines as deep as visual magnitude 16.0. [9]

The deep declines of DY Persei occur much more regularly than those of most R CrB stars, and they are generally symmetrical with slower decline and recovery rates than other R CrB stars. It is unclear whether it is really a member of the class or a pulsating asymptotic giant branch star with unrelated veiling ejections, [7] or just the cooler version of R CrB stars. [17]

Companion

There is a 14th magnitude star 2.5" from DY Persei, but it appears to be a chance alignment. It was not generally recognised until 2005, and would have strongly affected observations when DY Per was below maximum light. The companion is likely to be a G5 main sequence star much further away than DY Per. [9] It had been reported that the colour of DY Persei became more blue during a deep decline, highly unexpected for a star of this type, but this has been explained as the relatively increased contribution to the light from the companion as DY Persei itself becomes fainter. [7]

Spectrum

Image of the northwest corner of Perseus showing Comet Lovejoy and the Double Cluster. Trumpler 2 is on the left edge and DY Persei is visible as a faint red star nearby.
(Juan lacruz) Comet Lovejoy.jpg
Image of the northwest corner of Perseus showing Comet Lovejoy and the Double Cluster. Trumpler 2 is on the left edge and DY Persei is visible as a faint red star nearby.
(Juan lacruz)

DY Persei is a carbon star, with an excess of carbon relative to oxygen in its atmosphere. This causes dramatic changes in the atmospheric chemistry that are visible in the spectrum.

The spectral type under the original M-K carbon star system is C5,4pJ: (C54pJ:). This means that the spectrum overall is comparable to a late K or early M class, with strong C2 Swan bands. The "p" indicates that there are peculiarities and the "J" that there are isotopic bands from 13C. In the revised M-K system, the spectral type is C-R4+ C25.5. This describes essentially the same spectral features, although the C-R type indicates that the isotopic bands are strong but not sufficiently so to merit a "J". The exact 13C/12C ratio for DY Persei is disputed. S-process metal spectral lines are weak compared to other carbon stars, suggesting that DY Persei is not a thermally-pulsing asymptotic giant branch star. Overall, hydrogen spectral features are weak and metal lines typical, showing that DY Persei is hydrogen-deficient but not metal-poor. [9]

During deep minima, the carbon-related spectral bands become less prominent, and some emission lines are seen. In typical R CrB variables, the spectra at minimum show many strong emission lines of metals, but in DY Persei only a few are detected. A broad emission line of neutral sodium is seen, together with possible emission from neutral calcium and carbon. [9]

Properties

DY Persei is the larger of the two red stars in the center of this optical light image. DY Persei.jpg
DY Persei is the larger of the two red stars in the center of this optical light image.

DY Persei has a temperature around 3,000 K, but at a deep minimum its spectrum has been best modelled as the sum of two black body objects, one of 1,700 K typical of dusty circumstellar material and one of 2,400 K typical of the coolest giant stars. [7]

The size and luminosity of DY Persei, and other DY Persei and R Coronae Borealis stars, are very poorly known. [9] The absolute magnitude is thought to be around 2.5, about 855 times brighter than the sun. [7]

The metallicity of DY Persei has been reported to be much lower than solar, but other studies consider it to be near-solar. [12] [7]

Related Research Articles

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<span class="mw-page-title-main">T Coronae Borealis</span> Recurrent nova in the constellation Corona Borealis

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<span class="mw-page-title-main">UU Aurigae</span> Star in the constellation of Auriga

UU Aurigae is a carbon star in the constellation Auriga. It is approximately 341 parsecs from Earth.

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<span class="mw-page-title-main">R Coronae Borealis variable</span> Type of eruptive variable star

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<span class="mw-page-title-main">Epsilon Coronae Borealis</span> Multiple star system in the constellation Corona Borealis

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<span class="mw-page-title-main">Delta Coronae Borealis</span> Yellow giant star in the constellation Corona Borealis

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<span class="mw-page-title-main">Lambda Coronae Borealis</span> Yellow-white hued star in the constellation Corona Borealis

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<span class="mw-page-title-main">RY Sagittarii</span> Yellow supergiant star in the constellation Sagittarius

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<span class="mw-page-title-main">Z Ursae Minoris</span> Star in the constellation Ursa Minor

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References

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Further reading