Tau Ceti

Bayer name	τ Ceti
Flamsteed name	52 Ceti
Bonn survey	BD −16 ° 295
Bright Star Catalog	HR 509 [1]
Henry Draper Catalog	HD 10700 [2]
Gliese catalog	FY 71 [3]
Hipparcos catalog	HIP 8102 [4]
SAO catalog	SAO 147986 [5]
Tycho catalog	TYC 5855-2292-1 [6]
2MASS catalog	2MASS J01440402-1556141 [7]
Other names	FK5 59

Tau Ceti [ ˌtaʊ ˈʦeːti ] ( τ Ceti , abbreviated: τ Cet ) is a yellow main sequence star ( spectral class G8) in the constellation Whale, 11.9 light years away . Seen from the Sun it is to Alpha Centauri A of the second nearest sun-like star .

The star has no traditional proper name. The name "Tau Ceti" is a name according to the Bayer classification . Tau (τ) is the 19th Greek character , and "Ceti" indicates belonging to the constellation whale ( Latin: Cetus ).

Tau Ceti can be seen with the naked eye as a faint third magnitude star . Conversely, the sun from Tau Ceti would be a bit brighter in the constellation Bear Guardian . As with the Sun, most of the neighboring stars are faint red M dwarfs and are invisible to the naked eye from Tau Ceti. The closest neighbor of Tau Ceti is YZ Ceti at a distance of 1.6 ly . The second closest star system, Luyten 726-8 , is 3.19 ly away.

Tau Ceti has repeatedly been targeted as a target for the search for extraterrestrial intelligence ( SETI ). So far, with the help of astrometric methods and observation of radial velocity, indications of the existence of five planets with twice to six times the mass of the earth have been found, one of them in the habitable zone . Tau Ceti is surrounded by more than twelve times as much dust as our sun. Because of this disk of dust, which must also contain comets and asteroids , the planets are exposed to more impacts than the earth . Although this would greatly affect possible life, the resemblance to the sun attracted widespread interest.

Physical Properties

Tau Ceti is likely a single star. At an apparent distance of 137 arc seconds (according to measurements in 2000), however, there is a faint (13.1 ^m ) star that could be gravitationally bound to Tau Ceti.

The sun (left) is both larger and slightly hotter than the less active Tau Ceti (right, illustration).

Like the sun, Tau Ceti belongs to the spectral class G, but with G8 it has a somewhat later subtype than the sun with G2. This slight difference is due to the slightly lower surface temperature of around 5070 ° C (5344 ± 50K) compared to the sun. Both stars are main sequence stars of luminosity class V. As a result, they are in the stable phase of hydrogen combustion ( fusion of hydrogen to helium ). The deviations in the physical parameters between Tau Ceti and the Sun are essentially due to the different stellar masses. This is also reflected in the position of the stars to one another on the main sequence. The mass of Tau Ceti is about 0.77 solar masses. Therefore, the star will remain in the main sequence for about 12 billion years - one billion years longer than the sun .

Most of the parameters of the star's physical properties were determined by spectroscopic measurements. By comparing the spectrum with computer models of star formation and evolution, the star's mass, age, radius and luminosity can be determined. In addition, astronomical interferometers can measure the radius of Tau Ceti directly and fairly accurately. A long baseline is used to be able to resolve very small angles (much smaller than with conventional telescopes ). This made it possible to determine the radius of Tau Ceti to be 77.3 percent (± 0.02%) of the solar radius. This is roughly the size that can be expected for a star with 0.75 solar masses.

rotation

The rotation period of Tau Ceti was measured by periodic changes in the classical absorption lines H and K of the singly ionized calcium (Ca II). These lines are influenced by the magnetic activity on the surface, so that the observed period of variation is equal to the time required for the active areas to fully rotate around the star. In this way, a rotation period of 34 days was determined.

The rotation speed of a star influences the width of the absorption lines in the light spectrum due to the Doppler effect . Thus, by measuring the line width, the component of the rotational speed lying in the direction of the line of sight can be estimated. For Tau Ceti it amounts to:

{\ displaystyle v _ {\ text {eq}} \ cdot \ sin i \ \ approx \ 1 \, {\ text {km / s}}}

The speed at the equator is and indicates the (unknown) angle of inclination of the axis of rotation against the line of sight. The equatorial speed of 1 km / s results from the period of rotation and the radius of Tau Ceti, from which the inclination angle of about 42 ° can be estimated. For a typical G8 star, the speed of rotation is around 2.5 km / s. The relatively low value indicates that Tau Ceti is turning one of its poles towards the earth. ${\ displaystyle v _ {\ text {eq}}}$ ${\ displaystyle i}$ ${\ displaystyle i}$

The width of the absorption lines in the spectrum of a star is influenced not only by the rotation but also by the pressure broadening (see also spectral lines ). The radiation emitted by a single particle can be altered by the presence of other particles (e.g. impact). Therefore, the line width of the light spectrum is also dependent on the pressure on the surface of the star. The pressure, in turn, depends on the temperature and gravity. This relationship was used to determine the gravitational acceleration at the surface of Tau Ceti. This value is approximately g = 251 m / s ² and is therefore very close to the corresponding value for the sun ( g = 272.7 m / s ² ).

Metallicity

The chemical composition of a star provides important information about its development, especially when it was formed. The interstellar medium of dust and gas that stars form from consists primarily of hydrogen and helium with traces of heavier elements. As new stars continually emerge and fade, they continually enrich the interstellar medium with heavier elements. Therefore, younger stars tend to have higher proportions of heavier elements in their atmospheres than the older ones. These heavier elements are called "metals" by astronomers and the proportion of metals is called metallicity . The metallicity of a star is indicated by the ratio of iron (Fe) to hydrogen (H). The logarithm of the relative iron content is compared to that of the sun. In the case of Tau Ceti, the atmospheric metallicity is about

{\ displaystyle \ left [{\ frac {\ mathrm {Fe}} {\ mathrm {H}}} \ right] = - 0 {,} 52}

This corresponds to about a third (10 ^−0.52 ) of the proportion in the sun. Older measurements had given values between −0.13 and −0.60.

The lower level of iron indicates that Tau Ceti is older than the sun. Its estimated age is around 10 billion years. That is a considerable proportion of the age of the visible universe . For comparison: the sun is only 4.57 billion years old.

Luminosity and changeability

Since the luminosity of Tau Ceti is about 52 percent of the sun, the habitable zone is roughly between 0.6 and 0.9 astronomical units (AU). A planet would have to orbit Tau Ceti less than 0.7 AU to receive the same radiation as Earth in the solar system. That is just below the average distance from Venus to the sun.

The chromosphere - the layer of atmosphere immediately above the light-emitting photosphere - currently shows little to no magnetic activity. This indicates a stable star. A nine-year study of temperature, granulation, and chromosphere showed no systematic changes. Emissions in the H and K lines of Ca II indicated a possible 11-year cycle. This would be relatively weak compared to that of the sun. It has also been suggested that the star is in a transient state of low activity, comparable to the Maunder Minimum , the historic sunspot-free period that coincided with the Little Ice Age in Europe.

Dust disc

The unusually strong radiation emitted by the Tau-Ceti system in the far infrared region of the spectrum already indicates that the star is surrounded by a disk of dust. The dust particles are heated by the radiation from the star and in turn emit thermal radiation in the far-infrared spectral range. In 2004, a team of British astronomers, led by Jane Greaves, did indeed see a flat cloud of −210 ° C warm dust on high-resolution far-infrared images with the James Clerk Maxwell telescope on Mauna Kea (Hawaii). Since the dust particles are removed from the system in a relatively short time by the radiation pressure of the star and other mechanisms, such a dust disk can only be preserved for a longer period of time if it is constantly filled up by collisions between heavier bodies. Given the age of Tau Ceti, this dust is therefore the "abrasion" of already existing larger bodies ( debris disc ) and not the dust that was present shortly after the star formation, from which planets and other bodies are still to form. The disk forms a symmetrical structure around the star and has an outer radius of 55 AU. The absence of infrared radiation from warmer areas of the disk near Tau Ceti indicates a central gap with a radius of 10 AU. In comparison, the Kuiper Belt of the Solar System extends from 30 to 50 AU outside of Neptune's orbit.

The amount of dust in the disk around Tau Ceti is about twelve times that of the Kuiper Belt in the solar system. Based on this proportion, it can be concluded that there are around 1.2 earth masses on larger objects (> 10 km) in the disk. With this result, the hope of complex life in the Tau Ceti system is dampened because planets there are 10 times more likely serious impacts ( Impacts would face) than the Earth. Greaves remarked, "It is to be expected that [possible planets] would be subject to constant bombardment by asteroids similar to the one that presumably wiped out the dinosaurs ." However, if a gas giant the size of Jupiter existed in the system, it might Distract comets and asteroids and thus protect other planets.

Tau Ceti shows that stars do not have to lose their dust discs with increasing age. Thus, sun-like stars with a thick disk of dust are probably not uncommon. Nevertheless, according to current models, a gradual loss of dust can be expected. The dust density in the disk around Tau Ceti (4.4 to 12 billion years old) is, in accordance with the models, only 1/20 of the dust density that in the disk of its younger neighbor Epsilon Eridani (0.73 billion years old) ) is available. The sun, which lies between the two in terms of its age (4.5 billion years), however, has too little dust to fit into the series of the other two. That could mean that the sun is an exception here. It is possible that another star just passed the Sun when she was young, snatching most of the comets and asteroids away from it. Stars with pronounced debris disks have changed the way astronomers think about planet formation. Stars with debris disks, in which dust is constantly generated by collisions, appear to be suitable for forming planets.

Move

Tau Ceti's own movement (the movement component in the sky directed across the line of sight) is relatively high at almost 2 arc seconds per year and thus already an indicator of a relatively small distance to the sun. Because of its proximity, the distance to the star can be easily determined by measuring its parallax - it is 274.18 ± 0.80 mas (milliarcsecond = one thousandth of an arc second), which corresponds to 11.9 light years or 3.65 parsecs . This puts it in 23rd position in the list of the nearest stars .

The radial speed (the speed component in the direction of the observer's line of sight), in contrast to proper motion, cannot be observed directly; it must be determined by examining the spectrum . If the star moves away, the absorption lines of the star spectrum shift in the direction of longer wavelengths due to the Doppler effect. Similarly, the lines shift to shorter wavelengths if the star approaches. Tau Ceti's radial velocity is about −16 km / s. The negative sign means that the star is approaching the sun. In 43,000 years, the star will have reached its closest approach to the sun at 10.6 ly.

With the known distance, the proper motion and the radial velocity, the total motion of the star can be calculated. The result is a space velocity of 37 km / s relative to the sun. With this value one can calculate the orbit of Tau Ceti in the Milky Way . The orbit has an eccentricity of 0.22, which is relatively high for a star on the galactic disk, and an average distance from the center of the galaxy of 32,000 ly (9700 pc). The current distance from Tau Ceti to the galactic center corresponds to that of the Sun, 25,900 ly (7940 pc).

Search for planets and life

A major factor driving interest in Tau Cetis exploration is its sun-like properties and their importance to possible planets and life. This fact has inspired science fiction for decades . The fact that Tau Ceti is a single star could mean an advantage for planet formation, since planet formation is not disturbed by a second star. Since the star has existed for so long, there would have been enough time for complex life to emerge.

Search for planets

As early as 1988, an evaluation of long-term series of measurements of astrometry and radial velocity showed no direct evidence of a large companion ( Hot Jupiter ) in a narrow orbit, but only excluded the existence of companions with a mass greater than 4.2 Jupiter's masses.

The previous measurements of the radial velocity achieved an accuracy of 11 m / s over a period of 5 years and could rule out the existence of "Hot Jupiters" . A planet with more than one mass of Jupiter and an orbital period of less than 15 years can also be excluded. In addition, an investigation of nearby stars by the Hubble Space Telescope's Wide Field and Planetary Camera was completed in 1999 , which also included the search for weak companions of Tau Ceti. However, none could be found up to the detection limit of the telescope.

The absence of "Hot Jupiters" within the life zone is possibly an important prerequisite for the existence of Earth-like planets, since such planets would presumably not allow stable planetary orbits in a star orbit. The proof of the thick scree also increases the probability of terrestrial planets. On the other hand, statistical studies have shown that stars with lower metallicity like Tau Ceti are less likely to have planets.

The application of refined calculation methods to the radial velocity data of Tau Ceti now indicates the presence of five planets in dynamically stable orbits with orbital times of 13.9, 35.4, 94, 168 and 640 days. These exoplanets ( Tau Ceti b , Tau Ceti c , Tau Ceti d , Tau Ceti e and Tau Ceti f ) have the calculated masses of 2.0, 3.1, 3.6, 4.3 and 6.6 earth masses . The planet Tau Ceti e with an orbital period of 168 days would be in the habitable zone .

Search for life

Search for clues

In the future, telescopes such as the European Extremely Large Telescope, which is currently under construction, could look out for atmospheric water and life-friendly temperatures with even higher resolution. Life should make itself felt through an atmospheric composition that is atypical for inorganic processes. For example, the high oxygen content of the earth's atmosphere can be viewed as an indicator of life.

Search for intelligent life

The most targeted search project to date has been the Ozma project, which in 1960 listened to artificial radio signals from Tau Ceti and Epsilon Eridani to search for extraterrestrial intelligence ( SETI ) . It was directed by astronomer Frank Drake , who selected the two stars as targets because of their proximity and solar similarity. Despite 200 hours of observation, no artificial signals were found. Subsequent attempts to pick up signals from Tau Ceti have also been unsuccessful to this day.

However, these failed attempts have not dampened efforts to further examine the Tau-Ceti system for biosignatures. In 2002, astronomers Margaret Turnbull and Jill Tarter created the Catalog of Nearby Habitable Systems (HabCat) under the auspices of Project Phoenix (a SETI project ). This list contains more than 17,000 theoretically habitable systems, that is about 10 percent of the stars in the Hipparcos catalog. In the following year, Turnbull selected the 30 most promising (including Tau Ceti) from the 5000 systems that the catalog contained within 100 ly. This selection will be part of the working basis for radio surveys with the Allen Telescope Array . She also selected Tau Ceti as one of the five most suitable stars to be examined with the Terrestrial Planet Finder . She commented: "These are places where I would like to live if God would move our planet around another star."

Web links

Commons : Tau Ceti - collection of images, videos and audio files

What is going on in the Tau-Ceti System? from the alpha-Centauri television series(approx. 15 minutes). First broadcast on May 24, 2006.
The Hipparcos and Tycho Catalogs. European Space Agency, July 9, 2007, accessed on March 24, 2008 (English, type catalog number 8102 into the search field “Hipparcos Identifier”).
http://stars.astro.illinois.edu/sow/taucet.html

Remarks

↑ From Tau Ceti, the sun would be on the diametrically opposite side of the sky at the coordinates α 13 ^h 44 ^m 04 ^s , δ + 15 ° 56 ′ 14 ″ , i.e. near Tau Bootis . The absolute magnitude of the sun is 4.8 ^M . It appears bright from a distance of 3.64 parsecs .134404 2155614 ${\ displaystyle {\ begin {smallmatrix} m = M_ {v} +5 \ cdot ((\ log _ {10} 3 {,} 64) -1) = 2 {,} 6 ^ {\ mathrm {m}} \ end {smallmatrix}}}$

↑ This star could "just" happen to be in almost the same line of sight and actually be many light years away from Tau Ceti.

↑ Whether or not Jupiter actually offers protection for the inner solar system is still unclear. See e.g. E.g .: Jupiter: Friend or Foe?

↑ The proper motion is given by :, where and represent the two components of the proper motion in right ascension and declination and the declination.

{\ displaystyle {\ begin {smallmatrix} \ mu = {\ sqrt {{\ mu _ {\ delta}} ^ {2} + {\ mu _ {\ alpha}} ^ {2} \ cdot \ cos ^ {2 } \ delta}} = 1907 {,} 79 \, {\ text {mas / year}} \ end {smallmatrix}}}

{\ displaystyle \ mu _ {\ alpha}}

{\ displaystyle \ mu _ {\ delta}}

{\ displaystyle \ delta}

↑ The components of space velocity are: U = +18; V = +29; W = +13. This gives a net space velocity of

{\ displaystyle {\ begin {smallmatrix} {\ sqrt {18 ^ {2} + 29 ^ {2} + 13 ^ {2}}} = 36 {,} 5 \, {\ text {km / s.}} \ end {smallmatrix}}}

Individual evidence

↑ ^a ^b ^c Hipparcos catalog (ESA 1997)

↑ ^a ^b ^c Bright Star Catalog

↑ Pulkovo radial velocities for 35493 HIP stars

↑ ^a ^b ^c Hipparcos, the New Reduction (van Leeuwen, 2007)

↑ ^a ^b ^c ^d ^e FP Pijpers, TC Teixeira, PJ Garcia, MS Cunha, MJPFG Monteiro, J. Christensen-Dalsgaard: Interferometry and asteroseismology: The radius of T Ceti . In: Astronomy & Astrophysics . tape 401 , 2003, p. L15-L18 , doi : 10.1051 / 0004-6361: 20030837 ( aanda.org [accessed January 17, 2008]).

↑ ^a ^b E. Di Folco et al .: A near-infrared interferometric survey of debris disk stars. I. Probing the hot dust content around ɛ Eridani and τ Ceti with CHARA / FLUOR . In: Astronomy and Astrophysics . tape 475 , 2007, p. 243-250 , doi : 10.1051 / 0004-6361: 20077625 .

↑ ^a ^b ^c ^d NC Santos, G. Israelian, RJ García López, M. Mayor, R. Rebolo, S. Randich, A. Ecuvillon, C. Domínguez Cerdeña: Are beryllium abundances anomalous in stars with giant planets? In: Astronomy and Astrophysics . tape 427 , 2004, pp. 1085-1096 , arxiv : astro-ph / 0408108v1 .

^ ^A ^b S. Baliunas, D. Sokoloff, W. Soon: Magnetic Field and Rotation in Lower Main-Sequence Stars: an Empirical Time-dependent Magnetic Bode's Relation? In: Astrophysical Journal Letters . tape 457 , 1996, pp. L99 , doi : 10.1086 / 309891 , bibcode : 1996ApJ ... 457L..99B .

^ ^A ^b E. Di Folco, F. Thévenin, P. Kervella, A. Domiciano de Souza, V. Coudé du Foresto, D. Ségransan, P. Morel: VLTI near-IR interferometric observations of Vega-Like Stars . In: Astronomy and Astrophysics . tape 426 , 2004, p. 601–617 , doi : 10.1051 / 0004-6361: 20047189 , bibcode : 2004A & A ... 426..601D .

^ JC Hall, GW Lockwood: The Chromospheric Activity and Variability of Cycling and Flat Activity Solar-Analog Stars . In: The Astrophysical Journal . tape 614 , 2004, pp. 942-946 , doi : 10.1086 / 423926 .

↑ ^a ^b Tau Ceti. Sol Company, accessed September 25, 2007 .

↑ ^a ^b ^c ^d ^e ^f ^g JS Greaves, MC Wyatt, WS Holland, WRF Dent: The debris disc around tau Ceti: a massive analogue to the Kuiper Belt . In: Monthly Notices of the Royal Astronomical Society . tape 351 , no. 3 , 2004, p. L54-L58 , doi : 10.1111 / j.1365-2966.2004.07957.x .

^ CE Worley, GG Douglass: The Washington Visual Double Star Catalog, 1996.0 . In: A & A Supplement series . tape 125 , November 1, 1997, pp. 523–523 ( harvard.edu - open "I / 237 / catalog", type "Tau Ceti" in the "Target Name" field).

↑ SIMBAD Query Result: HD 10700 - High proper-motion star. Center de Données astronomiques de Strasbourg, accessed on January 17, 2008 .

↑ HK Project: Overview of Chromospheric Activity. (No longer available online.) Mount Wilson Observatory, archived from the original August 31, 2006 ; accessed on November 15, 2006 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.

^ ^A ^b DF Gray, SL Baliunas: The activity cycle of tau Ceti . In: Astrophysical Journal . tape 427 , no. 2 , 1994, p. 1042-1047 , doi : 10.1086 / 174210 .

↑ Jeffrey C. Hall, GW Lockwood, Erika L. Gibb: Activity cycles in cool stars. 1: Observation and analysis methods and case studies of four well-observed examples . In: Astrophysical Journal . tape 442 , no. 2 , 1995, p. 778-793 , doi : 10.1086 / 175483 .

^ ^A ^b G. Cayrel de Strobel, B. Hauck, P. Francois, F. Thevenin, E. Friel, M. Mermilliod, S. Borde: A catalog of Fe / H determinations - 1991 edition . In: Astronomy and Astrophysics Supplement Series . tape 95 , no. 2 , 1991, ISSN 0365-0138 , pp. 273-336 , bibcode : 1992A & AS ... 95..273C .

↑ G. Carraro, YK Ng, L. Portinari: Age Metallicity Relation and Star Formation History of the Galactic Disk . In: Monthly Notices of the Royal Astronomical Society . tape 296 , no. 4 , 1999, p. 1045-1056 , bibcode : 1997astro.ph..7185C .

↑ C. Flynn, O. Morell: Metallicities and kinematics of G and K dwarfs . In: Monthly Notices of the Royal Astronomical Society . tape 286 , no. 3 , 1997, p. 617-625 , bibcode : 1996astro.ph..9017F .

^ P. Frick, SL Baliunas, D. Galyagin, D. Sokoloff, W. Soon: Wavelet Analysis of Stellar Chromospheric Activity Variations . In: The Astrophysical Journal . tape 483 , no. 1 , 1997, p. 426-434 , doi : 10.1086 / 304206 .

^ Philip G. Judge, Steven H. Saar: The outer solar atmosphere during the Maunder Minimum: A stellar perspective . In: The Astrophysical Journal . tape 663 , no. 1 , July 18, 1995, p. 643-656 , doi : 10.1086 / 513004 .

↑ Philip G. Judge, Steven H. Saar, Mats Carlsson, Thomas R. Ayres: A Comparison of the Outer Atmosphere of the “Flat Activity” Star τ Ceti (G8 V) with the Sun (G2 V) and α Centauri A ( G2 V) . In: The Astrophysical Journal . tape 609 , no. 1 , 2004, p. 392-406 , doi : 10.1086 / 421044 .

↑ Tau Ceti in sustained fire. July 1, 2004, accessed March 25, 2008 .

↑ ^a ^b Maggie McKee: Life unlikely in asteroid-ridden star system. New Scientist , July 7, 2004, accessed on September 7, 2019 : “It is likely that [any planets] will experience constant bombardment from asteroids of the kind believed to have wiped out the dinosaurs. "

↑ ^a ^b Jane S. Greaves: Disks Around Stars and the Growth of Planetary Systems . In: Science (magazine) . tape 307 , no. 5706 , January 2005, p. 68-71 , doi : 10.1126 / science.1101979 .

↑ Steven R. Majewski: Stellar Motions. University of Virginia, 2006, accessed August 4, 2018 .

^ Neill Reid: Meeting the neighbors: NStars and 2MASS. Space Telescope Science Institute, February 23, 2002, accessed December 11, 2006 .

^ Todd J. Henry: The One Hundred Nearest Star Systems. Research Consortium on Nearby Stars, January 1, 2012, accessed December 18, 2017 .

↑ CAL Bailer-Jones: Close encounters of the stellar kind . In: Astronomy & Astrophysics . 575, March 2015, p. 13. arxiv : 1412.3648 . A35. bibcode : 2015A & A ... 575A..35B . doi : 10.1051 / 0004-6361 / 201425221 .

↑ GF Porto de Mello, EF del Peloso, L. Ghezzi: Astrobiologically interesting stars within 10 parsecs of the Sun . In: Astrobiology . tape 6 , no. 2 , 2006, p. 308–331 , doi : 10.1089 / ast.2006.6.308 .

^ F. Eisenhauer et al .: A Geometric Determination of the Distance to the Galactic Center . In: Astrophysical Journal . tape 597 , 2003, p. L121-L124 , doi : 10.1086 / 380188 .

↑ Spectral type G - Tau Ceti. Retrieved on March 25, 2008 (German).

↑ ^a ^b Bruce Campbell, GAH Walker: A Search for Substellar Companions to Solar-Type Stars . In: Astrophysical Journal . tape 331 , August 15, 1988, ISSN 0004-637X , p. 902-921 , bibcode : 1988ApJ ... 331..902C .

↑ Endl M .; Course student M .; Els S .: The planet search program at the ESO Coud'e Echelle spectrometer . In: Astron. Astrophys . tape 362 , 2002, pp. 585-594 , doi : 10.1051 / 0004-6361: 20020937 .

↑ Walker Gordon AH; Walker Andrew H .; Irwin W.Alan; et al. : A Search for Jupiter-Mass Companions to Nearby Stars . In: Icarus . tape 116 , 1995, pp. 359-375 , doi : 10.1006 / icar.1995.1130 .

↑ DJ Schroeder, DA Golimowski, RA Brukardt et al .: A Search for Faint Companions to Nearby Stars Using the Wide Field Planetary Camera 2 . In: Astronomical Journal . tape 119 , no. 2 , 2000, pp. 906-922 , doi : 10.1086 / 301227 .

^ G. Gonzalez: The Stellar Metallicity - Planet Connection . Ed .: ASP Conference Series 17-21. March 1997. bibcode : 1998bdep.conf..431G (English).

^ M. Tuomi: Signals embedded in the radial velocity noise, Periodic variations in the Tau Ceti velocities . ( herts.ac.uk [PDF; accessed December 19, 2012]).

^ Woolf Neville, J. Roger Angel: Astronomical Searches for Earth-like Planets and Signs of Life . In: Annual Review of Astronomy and Astrophysics . tape 36 , September 1998, pp. 507-537 , doi : 10.1146 / annurev.astro.36.1.507 .

↑ Amir Alexander: The Search for Extraterrestrial Intelligence, A Short History. The Planetary Society, 2006, archived from the original on August 29, 2007 ; Retrieved November 8, 2006 .

^ Margaret C. Turnbull, Jill Tarter: Target Selection for SETI. I. A Catalog of Nearby Habitable Stellar Systems . In: Astrophysical Journal Supplement Series . tape 145 , no. 1 , March 2003, p. 181-198 , doi : 10.1086 / 345779 .

^ Stars and Habitable Planets. Sol Company, accessed September 21, 2007 .

^ Earl Lane: Astronomer Margaret Turnbull: A Short-List of Possible Life-Supporting Stars. American Association for the Advancement of Science , January 18, 2006, accessed September 21, 2007 .

This article was added to the list of excellent articles on April 7, 2008 in this version .

[11] From Tau Ceti, the sun would be on the diametrically opposite side of the sky at the coordinates α 13 ^h 44 ^m 04 ^s , δ + 15 ° 56 ′ 14 ″ , i.e. near Tau Bootis . The absolute magnitude of the sun is 4.8 ^M . It appears bright from a distance of 3.64 parsecs .134404 2155614 ${\ displaystyle {\ begin {smallmatrix} m = M_ {v} +5 \ cdot ((\ log _ {10} 3 {,} 64) -1) = 2 {,} 6 ^ {\ mathrm {m}} \ end {smallmatrix}}}$

[15] This star could "just" happen to be in almost the same line of sight and actually be many light years away from Tau Ceti.

[28] Whether or not Jupiter actually offers protection for the inner solar system is still unclear. See e.g. E.g .: Jupiter: Friend or Foe?

[30] The proper motion is given by :, where and represent the two components of the proper motion in right ascension and declination and the declination. ${\ displaystyle {\ begin {smallmatrix} \ mu = {\ sqrt {{\ mu _ {\ delta}} ^ {2} + {\ mu _ {\ alpha}} ^ {2} \ cdot \ cos ^ {2 } \ delta}} = 1907 {,} 79 \, {\ text {mas / year}} \ end {smallmatrix}}}$ ${\ displaystyle \ mu _ {\ alpha}}$ ${\ displaystyle \ mu _ {\ delta}}$ ${\ displaystyle \ delta}$

[35] The components of space velocity are: U = +18; V = +29; W = +13. This gives a net space velocity of ${\ displaystyle {\ begin {smallmatrix} {\ sqrt {18 ^ {2} + 29 ^ {2} + 13 ^ {2}}} = 36 {,} 5 \, {\ text {km / s.}} \ end {smallmatrix}}}$

[hip1-1] Hipparcos catalog (ESA 1997)

[hr-2] Bright Star Catalog

[Pulkovo-3] Pulkovo radial velocities for 35493 HIP stars

[hip2-4] Hipparcos, the New Reduction (van Leeuwen, 2007)

[Pijpers2003-5] FP Pijpers, TC Teixeira, PJ Garcia, MS Cunha, MJPFG Monteiro, J. Christensen-Dalsgaard: Interferometry and asteroseismology: The radius of T Ceti . In: Astronomy & Astrophysics . tape 401 , 2003, p. L15-L18 , doi : 10.1051 / 0004-6361: 20030837 ( aanda.org [accessed January 17, 2008]).

[aa475-6] E. Di Folco et al .: A near-infrared interferometric survey of debris disk stars. I. Probing the hot dust content around ɛ Eridani and τ Ceti with CHARA / FLUOR . In: Astronomy and Astrophysics . tape 475 , 2007, p. 243-250 , doi : 10.1051 / 0004-6361: 20077625 .

[aa427Santos-7] NC Santos, G. Israelian, RJ García López, M. Mayor, R. Rebolo, S. Randich, A. Ecuvillon, C. Domínguez Cerdeña: Are beryllium abundances anomalous in stars with giant planets? In: Astronomy and Astrophysics . tape 427 , 2004, pp. 1085-1096 , arxiv : astro-ph / 0408108v1 .

[ApJL457-8] A ^b S. Baliunas, D. Sokoloff, W. Soon: Magnetic Field and Rotation in Lower Main-Sequence Stars: an Empirical Time-dependent Magnetic Bode's Relation? In: Astrophysical Journal Letters . tape 457 , 1996, pp. L99 , doi : 10.1086 / 309891 , bibcode : 1996ApJ ... 457L..99B .

[aa426-9] A ^b E. Di Folco, F. Thévenin, P. Kervella, A. Domiciano de Souza, V. Coudé du Foresto, D. Ségransan, P. Morel: VLTI near-IR interferometric observations of Vega-Like Stars . In: Astronomy and Astrophysics . tape 426 , 2004, p. 601–617 , doi : 10.1051 / 0004-6361: 20047189 , bibcode : 2004A & A ... 426..601D .

[hall1-10] JC Hall, GW Lockwood: The Chromospheric Activity and Variability of Cycling and Flat Activity Solar-Analog Stars . In: The Astrophysical Journal . tape 614 , 2004, pp. 942-946 , doi : 10.1086 / 423926 .

[SolStation-12] Tau Ceti. Sol Company, accessed September 25, 2007 .

[Greaves-13] ↑ ^a ^b ^c ^d ^e ^f ^g JS Greaves, MC Wyatt, WS Holland, WRF Dent: The debris disc around tau Ceti: a massive analogue to the Kuiper Belt . In: Monthly Notices of the Royal Astronomical Society . tape 351 , no. 3 , 2004, p. L54-L58 , doi : 10.1111 / j.1365-2966.2004.07957.x .