View source for Astronomy:IRAS 08544−4431

{{Short description|Variable star in the constellation Vela}}
{{Starbox begin
| name = IRAS 08544−4431
}}
{{Starbox image
| image=[[File:V390 Velorum - VLTI-R10µmB2µm.png|280px]]
| caption=Warm circumstellar material around IRAS 08544-4431
| credit=ESO
}}
{{Starbox observe
| epoch       = [[Astronomy:J2000.0|J2000.0]]
| constell    = [[Astronomy:Vela (constellation)|Vela]]
| ra          = {{RA|08|56|14.181}}<ref name=tycho2/>
| dec         = {{DEC|−44|43|10.71}}<ref name=tycho2/>
| appmag_v    = 9.01 - 9.19<ref name=gcvs/>
}}
{{Starbox character
| class       = F3e<ref name=maas/>
| b-v         =
| u-b         =
| variable    = [[Astronomy:RV Tauri variable|RV]]<ref name=gcvs/>
}}
{{Starbox astrometry
| radial_v    = +62.5<ref name=maas/>
| prop_mo_ra  = −7.8<ref name=tycho2/>
| prop_mo_dec = +9.5<ref name=tycho2/>
| parallax    = 0.6551
| p_error     = 0.0767
| parallax_footnote = <ref name=dr2/>
| dist_pc =
| absmag_v    = 
}}
{{Starbox orbit
| reference = <ref name=kluska/>
| period_unitless = {{val|506.0|1.3|ul=days}}
| axis = 
| eccentricity = {{val|0.22|0.02}}
| inclination = {{val|20|7.5}}
| node =
| periastron = 
| periarg = {{val|41.7|6.3}}
| k1 = {{val|8,7|0.2}}
}}
{{Starbox detail
| component1 = A
| age_gyr     =
| metal_fe    = &minus;0.5<ref name=maas/>
| mass        = 0.65<ref name=bujarrabal/>
| radius      = 75<ref name=kluska/>
| rotational_velocity =
| luminosity  = 14,000<ref name=kluska/>
| temperature = 7,250<ref name=stasinska/>
| gravity = 1.5<ref name=stasinska/>
| component2 = B
| mass2 = 1.15<ref name=bujarrabal/>
| temperature2 = 4,000<ref name=hillen/>
}}
{{Starbox catalog
}}
{{Starbox reference
|Simbad=V390+Velorum
}}
{{Starbox end}}

'''IRAS 08544−4431''' is a [[Astronomy:Binary system|binary system]] surrounded by a dusty ring in the constellation of [[Astronomy:Vela (constellation)|Vela]].  The system contains an [[Astronomy:RV Tauri variable|RV Tauri variable]] star and a more massive but much less luminous companion.

==Binary==
[[File:The dusty ring around the aging double star IRAS 08544-4431.jpg|thumb|left|upright=1.3|The dusty ring around IRAS 08544−4431]]
In 2003, IRAS 08544−4431 was being studied as a likely RV Tauri variable and was identified as a binary star from periodic variations in its observed [[Astronomy:Radial velocity|radial velocity]].  The primary is a luminous F3 star surrounded by a dusty disc, and the invisible secondary is a less massive star.

The two components of IRAS 08544−4431 orbit in 499 days in a mildly eccentric orbit. The projected semi-major axis is 0.32 AU but the inclination of the orbit is not known so the actual separation may be considerably larger, although the inclination is thought to be fairly large because the type of brightness variation implies a face-on system.<ref name=maas/>

==Variability==
[[File:V390VelLightCurve.png|thumb|left|A visual band light curve for V390 Velorum, adapted from Mass ''et al.'' (2003)<ref name=maas/>]]
IRAS 08544-4431 is classified as an RV Tauri star, a type of pulsating variable star which shows cycles with alternating shallow and deep minima. In addition, IRAS 08544-4431 shows slow variations in amplitude from cycle to cycle over approximately 1,600 days, a defining characteristic of a type b RV Tauri variable. The maximum amplitude is only 0.18 magnitudes.<ref name=kiss/> It was given the [[Astronomy:Variable star designation|variable star designation]] of V390 Velorum in 2006.<ref name=ibvs/>

The period, defined for an RV Tau star as the time between two deep minima, is 72 days. The slow variations in amplitude have been measured, represented by a period of 69 days producing beats. None of these variations correspond to the orbital motion.<ref name=kiss/>

==Post-AGB==
The primary star is thought to be a post-AGB star, a highly evolved star that has ceased fusion and is ejecting its outer layers on its way to becoming a [[Astronomy:White dwarf|white dwarf]]. Although many post-AGB stars become [[Astronomy:Planetary nebula|planetary nebula]]e once they become hot enough to ionise their ejected outer layers, it is thought that IRAS 08544−4431 is not massive enough to do this.<ref name=stasinska/>

==Dusty disc==
[[File:V390 Velorum.jpg|thumb|left|upright=1.4|The disc around IRAS&nbsp;08544−4431 at 2μm and 10μm. Although the image resembles a doughnut lit from the front, the brightest arc is the inner wall of the far side of the disc, lit by the stars at the centre.]]
The warm material surrounding IRAS 08544−4431 has been resolved using [[Astronomy:Interferometry|interferometry]] with the [[Engineering:AMBER (Very Large Telescope)|AMBER]] and MIDI instruments at the [[Astronomy:Very Large Telescope|Very Large Telescope]]. It is a circumbinary disc surrounding both stars, is heated mainly by the primary post-AGB star, and has a total mass of {{solar mass|0.015}}. The disc starts 9 AU from the stars and is approximately 4 AU thick at its inner edge. The thick disc protects much of the dust from direct heating out to 70 AU from the stars. Beyond 70 AU, the disc is thick enough to receive direct radiation from the stars.<ref name=deroo/>

The disc is at a temperature of 1,150 K. Although the companion is far less luminous than the primary, it is brighter than expected, especially at [[Physics:Infrared|infrared]] wavelengths. It is suspected to be a [[Astronomy:Main sequence|main sequence]] star with its own compact accretion disc. The best images of the disc and stars, taken using the [[Astronomy:PIONIER (VLTI)|PIONIER]] interferometer, show the primary star to be 0.5 mas across, the secondary to be an unresolved point source 0.91 mas away, and the circumbinary disc to be 14.15 mas in diameter. The disc is oriented at 19° to the plane of the sky aligned at an angle of about 6° away from N-S.<ref name=hillen/>

==References==
{{reflist|refs=

<ref name=ibvs>{{cite journal| bibcode=2006IBVS.5721....1K| title=The 78th Name-List of Variable Stars| journal=Information Bulletin on Variable Stars| volume=5721| pages=1| last1=Kazarovets| first1=E. V.| last2=Samus| first2=N. N.| last3=Durlevich| first3=O. V.| last4=Kireeva| first4=N. N.| last5=Pastukhova| first5=E. N.| year=2006}}</ref>

<ref name=maas>{{cite journal| bibcode=2003A&A...405..271M| arxiv=astro-ph/0306492| title=IRAS 08544-4431: A new post-AGB star in a binary system surrounded by a dusty disc| journal=Astronomy and Astrophysics| volume=405| pages=271–283| last1=Maas| first1=T.| last2=Van Winckel| first2=H.| last3=Lloyd Evans| first3=T.| last4=Nyman| first4=L.-Å.| last5=Kilkenny| first5=D.| last6=Martinez| first6=P.| last7=Marang| first7=F.| last8=Van Wyk| first8=F.| year=2003| doi=10.1051/0004-6361:20030613| s2cid=14743333}}</ref>

<ref name=tycho2>{{cite journal| bibcode=2000A&A...355L..27H| title=The Tycho-2 catalogue of the 2.5 million brightest stars| journal=Astronomy and Astrophysics| volume=355| pages=L27| last1=Høg| first1=E.| last2=Fabricius| first2=C.| last3=Makarov| first3=V. V.| last4=Urban| first4=S.| last5=Corbin| first5=T.| last6=Wycoff| first6=G.| last7=Bastian| first7=U.| last8=Schwekendiek| first8=P.| last9=Wicenec| first9=A.| year=2000}}</ref>

<ref name=gcvs>{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|display-authors=0|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref>

<ref name=stasinska>{{cite journal| bibcode=2006A&A...450..701S| arxiv=astro-ph/0601504| title=Post-AGB stars as testbeds of nucleosynthesis in AGB stars| journal=Astronomy and Astrophysics| volume=450| issue=2| pages=701| last1=Stasińska| first1=G.| last2=Szczerba| first2=R.| last3=Schmidt| first3=M.| last4=Siódmiak| first4=N.| year=2006| doi=10.1051/0004-6361:20053553| s2cid=12040452}}</ref>

<ref name=deroo>{{cite journal| doi=10.1051/0004-6361:20078079| title=AMBER and MIDI interferometric observations of the post-AGB binary IRAS 08544-4431: The circumbinary disc resolved| journal=Astronomy & Astrophysics| volume=474| issue=3| pages=L45| year=2007| last1=Deroo| first1=P.| last2=Acke| first2=B.| last3=Verhoelst| first3=T.| last4=Dominik| first4=C.| last5=Tatulli| first5=E.| last6=Van Winckel| first6=H.|bibcode = 2007A&A...474L..45D | url=https://lirias.kuleuven.be/bitstream/123456789/251484/1/Deroo2007.pdf| doi-access=free}}</ref>

<ref name=kiss>{{cite journal| bibcode=2007MNRAS.375.1338K| arxiv = astro-ph/0612217| title = Defining the instability strip of pulsating post-AGB binary stars from ASAS and NSVS photometry| journal = Monthly Notices of the Royal Astronomical Society| volume = 375| issue = 4| pages = 1338–1348| last1 = Kiss| first1 = L. L.| last2 = Derekas| first2 = A.| last3 = Szabó| first3 = Gy. M.| last4 = Bedding| first4 = T. R.| last5 = Szabados| first5 = L.| year = 2007| doi = 10.1111/j.1365-2966.2006.11387.x| s2cid = 14716983}}</ref>

<ref name=hillen>{{cite journal| bibcode=2016A&A...588L...1H| arxiv=1603.03023| title=Imaging the dust sublimation front of a circumbinary disk| journal=Astronomy & Astrophysics| volume=588| pages=L1| last1=Hillen| first1=M.| last2=Kluska| first2=J.| last3=Le Bouquin| first3=J.-B.| last4=Van Winckel| first4=H.| last5=Berger| first5=J.-P.| last6=Kamath| first6=D.| last7=Bujarrabal| first7=V.| year=2016| doi=10.1051/0004-6361/201628125| s2cid=118501739}}</ref>

<ref name=kluska>{{cite journal |bibcode=2018A&A...616A.153K |title=The perturbed sublimation rim of the dust disk around the post-AGB binary IRAS08544-4431 |journal=Astronomy and Astrophysics |volume=616 |pages=A153 |last1=Kluska |first1=J. |last2=Hillen |first2=M. |last3=Van Winckel |first3=H. |last4=Manick |first4=R. |last5=Min |first5=M. |last6=Regibo |first6=S. |last7=Royer |first7=P. |last8=van Wyk |first8=F. |year=2018 |arxiv=1805.04501 |doi=10.1051/0004-6361/201832983 |s2cid=119094976 }}</ref>

<ref name=bujarrabal>{{cite journal|bibcode=2018A&A...614A..58B|title=High-resolution observations of IRAS 08544-4431. Detection of a disk orbiting a post-AGB star and of a slow disk wind|journal=Astronomy and Astrophysics|volume=614|pages=A58|last1=Bujarrabal|first1=V.|last2=Castro-Carrizo|first2=A.|last3=Winckel|first3=H. Van|last4=Alcolea|first4=J.|last5=Contreras|first5=C. Sánchez|last6=Santander-García|first6=M.|last7=Hillen|first7=M.|last8=van Wyk|first8=F.|year=2018|arxiv=1802.04019|doi=10.1051/0004-6361/201732422|pmid=29983449|pmc=6031302}}</ref>

<ref name=dr2>{{cite Gaia DR2|5331400427026098816}}</ref>

}}


{{DEFAULTSORT:IRAS 08544-4431}}
[[Category:F-type stars]]
[[Category:Objects with variable star designations|Velorum, V390]]
[[Category:IRAS catalogue objects]]
[[Category:2MASS objects|J08561419−4443107]]
[[Category:Vela (constellation)]]
[[Category:RV Tauri variables]]
[[Category:Binary stars]]
[[Category:Post-asymptotic-giant-branch stars]]
[[Category:Emission-line stars]]
[[Category:Durchmusterung objects]]

{{Sourceattribution|IRAS 08544−4431}}