gamma Trianguli Australis

{{short description|Star in the constellation Triangulum Australe}}

{{Starbox image

| image =

{{Location mark

| image=Triangulum Australe IAU.svg

| float=center | width=250 | position=right

| mark=Red circle.svg | mark_width=10 | mark_link=γ TrA

| x%=59.0 | y%=54.6

}}

| caption=Location of γ Trianguli Australis (circled)

}}

{{Starbox observe

| epoch = J2000.0

| ra = {{RA|15|18|54.58129}}

| dec = {{DEC|−68|40|46.3680}}

| appmag_v = +2.87

| constell = Triangulum Australe

}}

{{Starbox character

| type = Subgiant

| class = A1III

| b-v = +0.00

| u-b = −0.02

| variable =

}}

{{Starbox astrometry

| radial_v = −3.0

| prop_mo_ra = −65.816

| prop_mo_dec = −31.187

| pm_footnote =

| parallax = 17.1809

| p_error = 0.3327

| parallax_footnote =

| dist_footnote =

| absmag_v = −0.89

}}

{{Starbox detail

| source =

| mass = 3.04

| radius = 6.5 or 7

| metal_fe =

| gravity = 3.39

| age_myr = 350

| luminosity = 249

| temperature = 8,225

| rotational_velocity = 199

}}

{{Starbox catalog

| names = {{odlist | B=γ TrA | CD=−68°1503 | FK5=560 | HD=135382 | HIP=74946 | HR=5671 | SAO=253097 }}

}}

{{Starbox reference

| Simbad = gam+TrA

}}

Gamma Trianguli Australis, Latinized from γ Trianguli Australis, is a white-hued star in the southern constellation of Triangulum Australe. Along with Alpha and Beta Trianguli Australis it forms a prominent triangular asterism that gives the constellation its name (Latin for southern triangle). It is the third-brightest member of this constellation with an apparent visual magnitude of +2.87. Based upon parallax measurements, Gamma Trianguli Australis is located at a distance of about {{Convert|190|ly|pc|abbr=off|lk=on}} from Earth.

Characteristics

The spectrum of this star matches a stellar classification of A1 III, which identifies it as a giant star. It could be also a subgiant. An unusual abundance of the element europium demonstrates it to be a peculiar, or Ap star. However, its classification as a chemically peculiar star is doubtful. Most stars of this type are slow rotators, but Gamma Trianguli Australis displays a very high rate of rotation with a projected rotational velocity of 199 km s⁻¹.

At a mass of 3.04{{Nbsp}}solar masses, Gamma Trianguli Australis was a late B-type star (B8V/B9V) in the main sequence. Being 350 million years old, it has recently begun its expansion towards a red giant. Its radius is either {{Solar radius|7|link=y}} (estimated using stellar isochrones) or {{Solar radius|6.5|link=y}} (measured). The star is emitting a luminosity equivalent to 250{{nbsp}}solar luminosities. Its surface has an effective temperature of {{val|8225|fmt=commas|ul=K}}. This is around {{val|2450|fmt=commas|ul=K}} hotter than the Sun{{Cite web |title=Sun Fact Sheet |url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html |website=nssdc.gsfc.nasa.gov}} and gives it a white hue, typical of A-type stars.

This star shows an excess emission of infrared radiation, suggesting that there is a circumstellar disk of dust orbiting this star. The mean temperature of the emission is 50 K, corresponding to a separation from the star of 481 astronomical units.

Reported companion star

The Gaia Data Release 3 (Gaia DR3) reported Gamma Trianguli Australis as an astrometric binary with a period of {{convert|488|day|year|abbr=off}}. The companion star would be a red dwarf with a mass of {{Solar mass|0.26}} and a semimajor axis of {{Val|1.8|ul=AU}}. However, a further study using the Very Large Telescope did not find any evidence of a companion, placing constraints on the properties of the putative companion.

Modern legacy

γ TrA appears on the flag of Brazil, symbolising the state of Paraná.{{cite web

|title=Astronomy of the Brazilian Flag

|url=https://flagspot.net/flags/br_astro.html

|publisher=FOTW Flags Of The World website

}}

References

{{Reflist|30em|refs=

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{{citation | last1=Royer | first1=F. | last2=Zorec | first2=J. | last3=Gómez | first3=A. E. | title=Rotational velocities of A-type stars. III. Velocity distributions | journal=Astronomy and Astrophysics | volume=463 | issue=2 | pages=671–682 |date=February 2007 | doi=10.1051/0004-6361:20065224 | bibcode=2007A&A...463..671R |arxiv = astro-ph/0610785 | s2cid=18475298 }}

{{cite journal | display-authors=1 | last1=Johnson | first1=H. L. | last2=Iriarte | first2=B. | last3=Mitchell | first3=R. I. | last4=Wisniewskj | first4=W. Z. | title=UBVRIJKL photometry of the bright stars | journal=Communications of the Lunar and Planetary Laboratory | volume=4 | issue=99 | date=1966 | page=99 | bibcode=1966CoLPL...4...99J }}

{{Cite journal |last1=Waisberg |first1=Idel |last2=Klein |first2=Ygal |last3=Katz |first3=Boaz |date=May 2024 |title=Hidden Companions to Intermediate-mass Stars. XIX. Spin–Orbit Misalignment and a 0.26M⊙, 1.8 au Companion in the Astrometric Binary Gamma Trianguli Australis* |url= |journal=Research Notes of the AAS |language=en |volume=8 |issue=5 |pages=131 |bibcode=2024RNAAS...8..131W |doi=10.3847/2515-5172/ad4a7b |doi-access=free |issn=2515-5172}}

{{citation | display-authors=1 | last1=Rhee | first1=Joseph H. | last2=Song | first2=Inseok | last3=Zuckerman | first3=B. | last4=McElwain | first4=Michael | title=Characterization of Dusty Debris Disks: The IRAS and Hipparcos Catalogs | journal=The Astrophysical Journal | volume=660 | issue=2 | pages=1556–1571 |date=May 2007 | doi=10.1086/509912 | bibcode=2007ApJ...660.1556R |arxiv = astro-ph/0609555 | s2cid=11879505 }}

{{cite web |title=The Colour of Stars |url=https://www.atnf.csiro.au/outreach/education/senior/astrophysics/photometry_colour.html |website=Australia National Telescope Facility |date=6 March 2024 |access-date=2024-05-27 }}

{{citation | last1=Sokolov | first1=N. A. | title=Effective temperatures of AP stars | journal=Astronomy and Astrophysics Supplement | volume=130 | pages=215–222 |date=June 1998 | issue=2 | doi=10.1051/aas:1998226 | bibcode=1998A&AS..130..215S | doi-access=free }}

{{citation | last1=Abt | first1=Helmut A. | last2=Morrell | first2=Nidia I. | title=The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars | journal=Astrophysical Journal Supplement | volume=99 | page=135 |date=July 1995 | doi=10.1086/192182 | bibcode=1995ApJS...99..135A | doi-access=free }}

{{citation | title=gam TrA -- Variable Star | work=SIMBAD Astronomical Object Database | publisher=Centre de Données astronomiques de Strasbourg | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Gamma+Trianguli+Australis | accessdate=2012-02-04 }}

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| title=The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets

| journal=The Astrophysical Journal

| volume=804 | issue=2 | pages=146 | year=2015

| bibcode=2015ApJ...804..146D | doi=10.1088/0004-637X/804/2/146

| arxiv=1501.03154 | s2cid=33401607 | postscript=. }}

{{citation

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| journal=Astronomy & Astrophysics

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{{citation