Tau1 Eridana

τ ¹ Eridani - ( Latinized version of the Latin. Tau ¹ Eridani ) is the Bayer designation . The star also has a designation given by Flemsteed - 1 Eridani.

In Chinese astronomy, , the star refers to the constellation (昴 宿, pinyin : Mǎo Xiù) "Hairy Head" and enters into asterism , 天 苑 ( Tiān Yuàn which means “Celestial Meadows”), consisting of γ Eridanus , π Eridanus , δ Eridanus , ε Eridanan , ζ Eridanan , η Eridanan , π China , τ ¹ Eridanan, τ ² Eridan , τ ³ Eridan , τ ⁴ Eridan , τ ⁵ Eridan , τ ⁶ Eridan , τ ⁷ Eridan , τ ⁸ Eridan, and τ ⁹ Eridan ^[16] . Therefore, τ ¹ Eridan itself is known as 天 苑 九 ( Tiān Yuàn jiǔ , the English The Eighth Star of Celestial Meadows - "The Eighth Star of Heavenly Meadow") ^[17] .

The spectral class of Tau ¹ Eridan is F7V ^[7] , which means that it is slightly larger ( 1 28${\displaystyle {\mathrm{<span\; class="nowrap"><span><span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">R</span></span></span></span>}}_{<span\; class="nowrap"><span><span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">⨀</span></span></span></span>}}$ {\ displaystyle R _ {\ bigodot}}   ^[9] ) and brighter than the Sun ( 2.78${\displaystyle {\mathrm{<span\; class="nowrap"><span><span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">L</span></span></span></span>}}_{<span\; class="nowrap"><span><span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">⨀</span></span></span></span>}}$ {\ displaystyle L _ {\ bigodot}}   ^[9] ), also this indicates that the star uses hydrogen in its core as a nuclear “fuel”, i.e. located on the main sequence . A star radiates energy from its external atmosphere at an effective temperature of about 6,231 K ^[11] , which gives it a yellow-white tint of an F-type star .

In order for our Earth to receive about the same amount of heat from the Sun, it must be placed at a distance of 1.67 AU (i.e., almost beyond the orbit of Mars ). Moreover, from such a distance the size of Tau ¹ Eridanus would look almost like our Sun from the Earth - 0.41 °, compared with the angular diameter of our Sun - 0.5 °., However, no planets have yet been discovered in the star ^[9] .

The star has a surface gravity of 4.34 GHS ^[11] or 218 8 m / s ² , i.e. slightly less than solar ( 274 0 m / s ² ). Stars with planets tend to be more metallic than the Sun, while Tau ¹ Eridanus is less metallic : its iron content relative to hydrogen is 83% of the solar. Rotating at an equatorial speed of 28.02 km / s ^[12] (that is, at a speed of almost 14 times that of the sun), this star needs about 2.7 days to complete a revolution, which apparently causes significant magnetic activity . Tau ¹ Eridanus is 1 8 billion years old , which is very dumb compared to the life of dwarfs with hydrogen “burning”, which is estimated at 4 9 billion years ^[10] .

Eridan's Tau ¹ shows an excess of radiation in the mid-far infrared at wavelengths of 12, 25, 60, and 100 μm , which was discovered by the Infrared Astronomical Observatory ( IRAS ) and published in 1993 ^[18] . This suggests that a cold residual disk with a radius of about 500 AU rotates around the star . . It was also suggested that if the stellar system were observed at longer waves, it is likely that the residual disk would have a radius much larger than 500 AU ^[19] . Later observations of the Spitzer space telescope published in 2004 did not reveal a significant excess of infrared radiation around the star in the wavelength range of 14–35 μm ^[20] .

Tau ^{1 of} Eridanus has a close satellite, of which nothing is known, except for a spectroscopically determined orbital period of 958 days ^[21] (the orbital period of Mars is 686 98 days ). Assuming that this satellite has less mass. Kepler’s laws show that Tau ¹ Eridanus B revolves around Tau ¹ Eridan A at a distance of 2 AU . If Tau ¹ Eridanus B makes any contribution to the system of Tau ¹ Eridanes, then this means that Tau ¹ Eridanas A has an even lower luminosity and mass than indicated above. It is possible that Tau ¹ Eridan B is a dwarf of spectral class K and rotates at a speed of 35.3 km / s ^[21] .

Tau ¹ Eridanus also has a belt, which consists mainly of small bodies, i.e. material left over from the formation of the Tau ¹ Eridanus system and which may look like our own Kuiper belt (dust ring outside Neptune’s orbit). This belt can be at a distance of 50 to 100 AU and may indicate some kind of planetary system with two internal stars, although in fact nothing was found ^[10] .

The Tau ¹ Eridan movement itself, however, shows that the star is a visitor from another part of the Galaxy , because the star moves at a rather high speed - +26 km / s ^[15] relative to the Sun , which is almost two times more than that of the local stars of the Galactic disk . It also means that the star is moving away from the Sun.

The following stellar systems are within 20 light-years ^[22] of the Tau ¹ Eridanus system (included only: the closest star, the brightest (<6.5 ^m ), and notable stars). Their spectral classes are shown against the background of the colors of these classes (these colors are taken from the names of the spectral types and do not correspond to the observed colors of stars):

  02 ^h 45 ^m 06.18710 ^s , −18 ° 34 ′ 21.2149 ″