Debris Belts Around Vega

Transcription

1 Debris Belts Arund Vega Tpic: Explanets Cncepts: Infrared bservatins, debris disks, explanet detectin, planetary systems Missins: Spitzer, Herschel Crdinated by the NASA Astrphysics Frum An Instructr s Guide fr using the slide sets is available at the ASP website ducatin/resurces-fr-thehigher-educatin-audience/ 0

2 Vega is wearing 2 belts! Vega Infrared bservatins reveal the star Vega has a warm inner dust belt in additin t the previusly-bserved uter cld dust belt. The discvery can be explained by tw belts f leftver planetesimals whse nging cllisins prduce the detected dust--analgus t the Sun s asterid and Kuiper Belts. Culd this als suggest a similar planetary system fr Vega? Abve: Image f the debris disk arund the star Vega taken in infrared light with the Herschel Space Observatry. (Credit: Su et al., 2013) Right: Artist s illustratin f debris belt arund Vega. (Credit: NASA/JPL-Caltech) 1

3 Hw was the Discvery Made? uter belt inner belt The Spitzer Space Telescpe and the Herschel Space Observatry detected infrared light in excess f that expected frm the star alne. By cmparing Vega t similar stars, scientists subtracted the infrared emissin prduced by the star itself, leaving the emissin radiated by surrunding dust particles warmed by the star. Herschel Space Observatry infrared image f the debris disk arund the star Vega, after subtracting the light f the star Vega itself. (Credit: Su et al., 2013) The inner regin f infrared excess culd nt be reslved int a belt like the uter ne but the temperature f the dust is cnsistent with an asterid belt abut the same prprtinal distance distance frm Vega as urs is frm ur smaller Sun. 2

4 The Big Picture Scientists have fund ther stars with similar inner and uter debris belts, with the uter belt abut ten times farther frm the stars than the inner belt. One such star, HR8799, has been fund t have fur giant planets rbiting in the gap between belts. Our wn slar system als has fur giant planets rbiting between the rcky asterid belt and the icy Kuiper belt. N planets have yet been detected arund Vega, but if the star were eventually fund t have several giant planets in rbit, this may suggest a cmmn mdel fr hw stars frm planets and hw their planetary systems evlve. 3

5 Hw des this discvery change ur view? Other stars can hst planetary systems similar t the Sun. The uter belts f bth Vega and Sun are abut ten times mre distant frm the star than the inner belts. Our slar system has planets between debris belts, and Vega may have planets in the gap als. Multiple debris belts may be a clue t the presence f several planets. In this diagram, the Vega system (left) is cmpared t ur Slar system scaled up by a factr f fur (right). The inner asterid belt (range) and Kuiper belt (red) are similar in relative scale, with the distance frm the stars t the uter debris belts abut ten times greater than the inner belts. The true relative size f ur slar system is illustrated by the small drawing in the middle. Credit: NASA/JPL-Caltech Our slar system may nt be unique. 4

6 Press Release n this result: Resurces Q_13-006_Vega_Asterid_Belt.html Scientific Paper Su, et al., 2013, ApJ 763:118 Synpsis article Additinal Resurces Explanet resurce guide my-resurce-guides/the-search-fr-planetsarund-ther-stars/ AAS annuncement by Kate Su M Extraslar Planets Encyclpaedia 5

7 Debris Belts Arund Vega BONUS CONTENT 6

8 Why haven t we fund planets fr Vega? Vega is riented n the plane f the sky, s we re lking at ne f its ples, and its debris disk is seen face-n, nt edge n. We can t detect planets by the transit methd since they wuldn t pass in frnt f the star frm ur perspective. We can t detect planets by the Dppler methd because stars like Vega rtate very fast and have very few narrw lines in their spectra fr nticing the tiny shifts in line psitin caused by the gravitatinal tugs f planets. Image credit: NASA/JPL-Caltech Direct visual searches have turned up empty, suggesting rbiting planets are t small fr us t yet detect by this methd. The mre pwerful James Webb Space Telescpe r mre sensitive grundbased searches may eventually find Jupiter-sized r smaller planets rbiting in Vega s gap. 7

9 Cllected Instructr s Ntes, part 1 Vega is wearing 2 belts! (page 2 in this PDF) Debris Disk: a disk f small particles encircling a star r planet. Belts, disks, and rings are all debris disks. The Figure is the Herschel view f the whle system, where the star is very bright at the center The tw slid circles mark radii f 5 and 7, while the dashed circle marks a radius f 14 (representing the cld planetesimal ring). Hw was the Discvery Made? (page 3 in this PDF) Herschel = (an ESA* missin with NASA participatin) *ESA = Eurpean Space Agency Figure is the glwing dust image after the cntributin f the star has been taken ut. Arrws pint t the lcatin f the belts. Clrs represent intensity f light, frm bright (red) t faint (blue).the inner belt is nt reslved int a ring, but rather is detected as excess light at the star s psitin. Vega is viewed almst face-n. The Big Picture (page 4 in this PDF) Astrnmers study stars with varying characteristics t understand hw planetary systems evlve. Vega s system is similar t ur slar system, but Vega is different frm the Sun. Bth stars have cld, uter belts like ur Kuiper Belt (~50 K) Vega is yung(~ millin years ld), while the Sun is 4.6 billin years ld. Vega is bright (spectral type A), times mre luminus than the Sun The clear separatin f the belts culd be explained by the presence f planets clearing the gap. Indeed, HR 8799 is already knwn t have 4 planets in this regin. Hw des this discvery change ur view (page 5 in this PDF) Vega and the Sun all have a warm inner belt at ice/gas transitin temperature (~170K) and a cld uter belt at ~50K. The uter belt f Vega is abut 10X mre distant frm the star than the inner belt. The distance between ur Sun s (uter, clder) Kuiper and (warmer, inner) Asterid belts is als a 10:1 rati Mdel calculatins predict that several planets (smaller than Jupiter) maintain a dust-free zne by sweeping up material in that gap. Thus it is likely that several yet-undetected planets reside in the gap between Vega s belts. Culd duble belts be a hallmark f a multi-planet system? fcus future bservatins n similar systems! 8

10 Cllected Instructr s Ntes, part 2 Resurces (page 6 in this PDF) Cntributing Missins: Herschel Space Observatry: Spitzer Space Telescpe: Why haven t we fund planets fr Vega? (page 8 in this PDF) Each technique is sensitive t detecting planets with certain physical characteristics (size, distance frm star, inclinatin, etc). Astrnmers use all the evidence available t target their searches. Fr example, if there s indirect evidence such as in this case, astrnmers culd target direct bservatins. Subtleties in why we can t detect planets by the Dppler methd: early-type stars like Vega rtate very fast and have very few narrw spectral lines. This means it is very difficult t ntice any star wbble. The dminating reasn is simply line f sight. 9