TX Piscium (19 Piscium) is a variable

carbon star A carbon star (C-type star) is typically an asymptotic giant branch star, a luminous red giant, whose atmosphere contains more carbon than oxygen. The two elements combine in the upper layers of the star, forming carbon monoxide, which consumes mos ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Pisces Pisces may refer to: * Pisces, an obsolete (because of land vertebrates) taxonomic superclass including all fish * Pisces (astrology), an astrological sign * Pisces (constellation), a constellation **Pisces Overdensity, an overdensity of stars in ...

. It is amongst the reddest

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...

stars, with a significant reddish hue when seen in

binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...

. It is approximately 900

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s from

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Spectrum

TX Piscium is a very red star, 2.6 magnitudes fainter at blue wavelengths than in the middle of the visual range, and another 3.3 magnitudes fainter in the

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

. It has been given a

spectral class In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

C7,2, indicating a relatively cool carbon star with only modest C₂ band strength. It has alternately been classified as C-N5 C₂4, suggesting a warmer star with stronger C₂ bands. Spectral features have been observed to vary.

Variability

The

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of TX Piscium varies between +4.9 and +5.5 and it is classified as a

slow irregular variable A slow irregular variable (ascribed the GCVS types L, LB and LC) is a variable star that exhibit no or very poorly defined periodicity in their slowly changing light emissions. These stars have often been little-studied, and once more is learnt abo ...

. Photometry has shown some periodicity in the brightness of 224 days, and some spectral variation over 450 days, suggesting the star is not entirely irregular. The star apparently lies on the

period-luminosity relation In astronomy, a period-luminosity relation is a relationship linking the bolometric luminosity, luminosity of pulsating variable stars with their pulsation period. The best-known relation is the direct proportionality law holding for Classical Ceph ...

corresponding to

fundamental Fundamental may refer to: * Foundation of reality * Fundamental frequency, as in music or phonetics, often referred to as simply a "fundamental" * Fundamentalism, the belief in, and usually the strict adherence to, the simple or "fundamental" idea ...

mode pulsations, unusual for a low-amplitude semi-regular or irregular variable which usually pulsate in an

overtone An overtone is any resonant frequency above the fundamental frequency of a sound. (An overtone may or may not be a harmonic) In other words, overtones are all pitches higher than the lowest pitch within an individual sound; the fundamental i ...

. The angular diameter has been measured at around 10

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, although this varies depending on the observed

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

and the atmosphere appears to be highly asymmetric. There may be one or more "blobs" of ejected material near the star. Some observations show the angular diameter to change in synchrony with the

visual brightness Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target. The perception is not linear to luminance, ...

Properties

TX Piscium is a thermally-pulsing

asymptotic giant branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

(TP-AGB) star, which means that it is alternately fusing helium in a shell around its core and fusing hydrogen in a shell closer to its surface. Stars on the TP-AGB are generally unstable, with high mass loss and pulsations. The periodic flashes of the helium shell in a TP-AGB star are known as thermal pulses and cause the hydrogen shell to be extinguished. This creates strong convection and the third

dredge-up A dredge-up is any one of several stages in the evolution of some stars. By definition, during a ''dredge-up'', a convection zone extends all the way from the star's surface down to the layers of material that have undergone fusion. Consequently, th ...

(TDU) which brings helium fusion products such as

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

to the surface. After several TDUs, the abundance of carbon in the atmosphere begins to exceed that of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

and then the star is known as a carbon star. In TX Piscium, the carbon/oxygen ratio is calculated to be 1.03, which is at the low end of the scale of carbon stars. It is thought to be a relatively new carbon star. TX Piscium has a mass of approximately . Modelling of its observed properties suggest a mass between , while evolutionary models suggest a mass between . In particular, stars with a mass below are not expected to become carbon stars. The temperature of TX Piscium is thought to vary between 3,080 K at minimum visual brightness and 3,170 K at visual maximum. Similarly, its luminosity varies between . Many of its physical properties are uncertain due to uncertainty in its distance. The

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

parallax corresponds to a distance of 275 parsecs, but other estimates give distances as high as 315 parsecs.

References

{{Stars of Pisces Pisces (constellation) Slow irregular variables Piscium, 019 Carbon stars Asymptotic-giant-branch stars Piscium, TX Durchmusterung objects 117245 9004 223075