413:
average brightness was steadily increasing. It brightened by about two magnitudes between 1943 and 1970, and then began to fade. Examination of old photographic observations found that the star had been brightening since at least 1900, with extrapolations suggesting that the minimum had occurred around 1880. As it faded, FG Sagittae began to show periodic variations, at first a period of 80 days, but increasing to 130 days. In 1992, the periodic variations ceased and the brightness decreased by five magnitudes in only two months. Since then, it has continued to show occasional deep fading events, appearing much like an
401:
1641:
424:. The first reliable spectral class is B0 in 1930. Extrapolation of the brightness and colour indices suggest it may have been an O3 star in 1890. It then steadily cooled, with the spectral class becoming as late as K2 in the 1980s. The spectral class has since stayed as a G or K type supergiant, but there have been dramatic changes. The abundances of various elements have either increased or decreased:
303:
FG Sge, HIP 99527, PN ARO 169, ALS 10924, IRAS 20097+2010, PN G060.3-07.3, AN 377.1943, Hen 3-1844, JP11 5474, CSI+20-20097, Hen 2-457, LS II +20 19, TYC 1626-619-1, CSV 5066, Hen 1-5, 2MASS J20115606+2020044,
412:
In 1943, a star designated AN 377.1943 was discovered to be a previously-unknown variable star. It was designated CSV 5066 as a suspected variable, and then FG Sagittae as a confirmed variable star. At the time, its variations were described as being irregular, but it was soon noted that the
540:
brightness increased by a comparable amount. Models of the dust around the star suggest that the luminosity dropped sharply for a few hundred days as dust formed and was heated, but the underlying stellar luminosity was essentially constant and remained constant until at least 2001.
544:
The underlying properties of FG Sagittae changed on a timescale almost unheard-of for a star, from a small very hot post-asymptotic giant branch star becoming a white dwarf, to a hot supergiant and then a cool supergiant. This is believed to have been due to a
536:
When the star faded in 1992, it was obscured by dust formation and comparisons of temperature and luminosity became more difficult. The visual luminosity dropped by about five magnitudes, but the
385:(AGB) to move towards the hottest end of the "white dwarf cooling track". This thermal pulse is believed to have revived this aged star to once again, for a short time, behave as an AGB star.
432:
elements became less visible; and carbon-rich dust became strongly visible after 1992. Observations of the spectrum after 1992 are hindered by the dust formation, but the s-process and
494:. During the deep fades since 1992, even lower temperatures have been calculated, but these may represent observations of obscuring dust rather than the surface of the star itself.
1673:
269:
553:
or very late thermal pulse, depending on the exact timing. Models approximate the behaviour of FG Sagittae although there are still detailed discrepancies.
517:
by 1965. The luminosity then became more or less stable until 1992. As the star cooled and became more luminous, its radius increased from around one
41:
377:
star; this behavior is emphasized by a hydrogen deficiency typical for this class of stars. It has been proposed that this star has undergone a
1263:
686:
Van
Genderen, A. M.; Gautschy, A. (1995). "Deductions from the reconstructed evolutionary and pulsational history of FG Sagittae".
1185:
Taranova, O. G.; Shenavrin, V. I. (2013). "FG SGE: Evolution of the circumstellar dust shell ( JHKLM Photometry in 1985-2013)".
34:
370:. It started to pulsate when becoming an A-type star with a period of 15 days. This period later increased to over 100 days.
452:
23. This formed when FG Sagittae first left the asymptotic giant branch. FG Sagittae is now losing mass at about one
883:
Lawlor, T. M; MacDonald, J (2003). "Sakurai's Object, V605 Aquilae, and FG Sagittae: An
Evolutionary Sequence Revealed".
1693:
1288:
487:
549:
in a shell that had previously been inactive since the star left the asymptotic giant branch. This is known as a late
713:
Shenavrin, V. I.; Taranova, O. G.; Nadzhip, A. E. (2011). "Search for and study of hot circumstellar dust envelopes".
405:
374:
799:
1142:
Rosenbush, A. É.; Efimov, Yu. S. (2015). "Photometry, Spectrometry, and
Polarimetry of FG Sge in the Active State".
1683:
759:
Ducati, J. R. (2002). "VizieR Online Data
Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system".
1418:
786:
1283:
840:
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1272:
414:
382:
344:
459:
every million years and a dust shell has formed around the star. This may form a second planetary nebula.
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103:
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1256:
498:
468:
356:
277:
1678:
1194:
1151:
1108:
1089:
Jeffery, C. S.; Schönberner, D. (2006). "Stellar archaeology: The evolving spectrum of FG Sagittae".
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973:
938:
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818:
768:
722:
695:
611:
163:
645:
562:
996:
Gehrz, Robert D.; Woodward, Charles E.; Temim, Tea; Lyke, James E.; Mason, Christopher G. (2005).
1481:
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1098:
908:
808:
738:
627:
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433:
378:
86:
998:"The Development of a Steady State, Asymptotic Giant Branch Type, Circumstellar Wind around the
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27:
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147:
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62:
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1315:
857:
295:
155:
1072:
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1214:
1171:
742:
550:
420:
The spectrum of FG Sagittae when it was first noted as a variable star was that of a
352:
341:
49:
912:
631:
1559:
1345:
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224:
197:
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359:
125:
114:
75:
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1383:
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1206:
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734:
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Since 1992 the star has exhibited fadings and recoveries similar to that of a
348:
334:
237:
204:
170:
135:
950:
1533:
1515:
1499:
1466:
964:
Kukarkin, B. V. (1960). "An unusual variable star CSV 5066 = 377.1943 Sge".
429:
1241:
1614:
1598:
1103:
537:
565:, also known as V4334 Sgr, another presumed late thermal pulsing object.
54:
37:
30:
1581:
1476:
1471:
1231:
844:
592:
Van
Leeuwen, F. (2007). "Validation of the new Hipparcos reduction".
474:
316:
284:
217:
175:
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1045:
1026:
997:
904:
813:
1619:
606:
490:
during the 1980s show a slow decrease in temperature to as low as
399:
362:
in 1955. Since then it has expanded and cooled, becoming a yellow
304:
UBV M 50884, PK 060-07 1, AAVSO 2007+20
1298:
337:
1245:
795:
Data
Release 2: Summary of the contents and survey properties"
428:
became at least 25 times more abundant between 1967 and 1974;
1237:
AAVSO Variable Star of the Month. FG Sagittae: November 1998
501:
of FG Sagittae increased steadily from around 2,700
1232:
AAVSO Variable Star of the Month. FG Sagittae: June 2008
1046:"The remarkable evolution of the post-AGB star FG Sge"
366:
by 1991, and then further cooling to become an orange
351:. When first noted in 1943, it was identified to be a
929:
Hoffmeister, Cuno (1944). "171 neue Veränderliche".
1607:
1589:
1580:
1558:
1532:
1508:
1490:
1417:
1359:
1306:
1297:
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at the end of the 19th century to over 10,000
789:; et al. (Gaia collaboration) (August 2018).
924:
922:
681:
679:
677:
675:
673:
671:
669:
667:
665:
436:appear to have continued becoming more abundant.
1044:Jurcsik, Johanna; Montesinos, Benjamín. (1999).
1084:
1082:
1039:
1037:
1257:
471:of FG Sagittae in 1930 would have been about
381:(LTP) of helium fusion after having left the
355:, and it was found to be a hot, blue star of
80:+20° 20′ 04.3672″
8:
991:
989:
987:
761:CDS/ADC Collection of Electronic Catalogues
587:
585:
1586:
1555:
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1303:
1264:
1250:
1242:
1102:
1025:
878:
876:
874:
832:
822:
812:
605:
448:, Henize 1-5, around FG Sagittae, around
754:
752:
1674:Objects with variable star designations
581:
388:FG Sagittae is the central star of the
18:
7:
858:"Life and times of a chameleon star"
33:
486:by 1975. Detailed analysis of the
14:
650:International Variable Star Index
404:Light curve showing the onset of
16:Star in the constellation Sagitta
1640:
1639:
841:Gaia DR2 record for this source
482:in 1890, then cooling to about
154:0.7630 ± 0.2302
444:There is a very faint visible
1:
1073:10.1016/S1387-6473(99)00098-6
1289:Sagitta in Chinese astronomy
800:Astronomy & Astrophysics
488:spectral energy distribution
966:Astronomicheskij Tsirkulyar
834:10.1051/0004-6361/201833051
375:R Coronae Borealis variable
1710:
1121:10.1051/0004-6361:20047075
1091:Astronomy and Astrophysics
688:Astronomy and Astrophysics
624:10.1051/0004-6361:20078357
594:Astronomy and Astrophysics
526:in 1900 to about 184
1637:
1554:
1528:
1279:
1207:10.1134/S1063773713110078
1164:10.1007/s10511-015-9365-x
1006:The Astrophysical Journal
931:Astronomische Nachrichten
885:The Astrophysical Journal
735:10.1134/S1063772911010070
309:
301:
294:
290:
191:
186:
182:
141:
134:
97:
24:
1284:List of stars in Sagitta
1273:Constellation of Sagitta
951:10.1002/asna.19432740409
1542:HD 231701 b (Babylonia)
1113:2006A&A...459..885J
824:2018A&A...616A...1G
700:1995A&A...294..453V
616:2007A&A...474..653V
415:R Coronae Borealis star
406:R Coronae Borealis-type
383:asymptotic giant branch
87:Apparent magnitude
409:
347:at a distance of 4000
1053:New Astronomy Reviews
499:bolometric luminosity
478:, possibly as hot as
469:effective temperature
403:
357:stellar spectral type
283:4,467 - 45,000
174:(approx. 1,300
108:(O3 -) B4Ieq - K2Ib
1694:Emission-line stars
1199:2013AstL...39..781T
1156:2015Ap.....58...46R
1065:1999NewAR..43..415J
1018:2005ApJ...623.1105G
978:1960ATsir.209...21K
943:1944AN....274..176H
897:2003ApJ...583..913L
773:2002yCat.2237....0D
727:2011ARep...55...31S
434:rare earth elements
408:deep minima in 1992
310:Database references
243:2,692- 12,000
169:approx. 4,000
21:
426:s-process elements
410:
379:late thermal pulse
296:Other designations
104:Spectral type
19:
1684:Hipparcos objects
1651:
1650:
1633:
1632:
1576:
1575:
1550:
1549:
1524:
1523:
1187:Astronomy Letters
1002:Star FG Sagittae"
715:Astronomy Reports
328:
327:
1701:
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1104:astro-ph/0608542
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703:
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609:
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563:Sakurai's Object
493:
485:
481:
477:
450:visual magnitude
446:planetary nebula
440:Planetary nebula
390:planetary nebula
98:Characteristics
90:
70:
65:
25:Observation data
22:
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1704:
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1625:Necklace Nebula
1603:
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787:Brown, A. G. A.
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422:blue supergiant
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305:
268:0.2 - 2.2
258:Surface gravity
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223:0.9 - 184
210:
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173:
85:
68:
63:Right ascension
61:
26:
17:
12:
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5:
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1226:External links
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1027:10.1086/428569
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905:10.1086/345411
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860:. Newscientist
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600:(2): 653–664.
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569:V605 Aquilae
547:helium flash
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492:5,280 K
484:5,500 K
473:25,000
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20:FG Sagittae
1679:Supergiants
1193:(11): 781.
1012:(2): 1105.
368:K-type star
364:G-type star
349:light-years
331:FG Sagittae
278:Temperature
126:color index
115:color index
93:8.7 - 23.0
76:Declination
1658:Categories
1568:Messier 71
1534:Exoplanets
1097:(3): 885.
1059:(6): 415.
1000:Born Again
937:(4): 176.
891:(2): 913.
864:2017-09-27
814:1804.09365
655:2020-08-20
576:References
335:supergiant
260:(log
238:Luminosity
136:Astrometry
1516:Gaia17bpp
1361:Flamsteed
1215:121547285
1172:121128187
1150:(1): 46.
743:122700080
607:0708.1752
533:by 1992.
463:Evolution
430:iron peak
203:0.8
89: (V)
1645:Category
1615:Abell 63
1419:Variable
1316:α (Sham)
913:53532914
646:"FG Sge"
632:18759600
557:See also
538:infrared
531:☉
523:☉
515:☉
507:☉
457:☉
249:☉
229:☉
209:☉
164:Distance
148:Parallax
1669:Sagitta
1582:Nebulae
1195:Bibcode
1152:Bibcode
1129:9774324
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696:Bibcode
694:: 453.
612:Bibcode
345:Sagitta
340:in the
187:Details
55:Sagitta
38:J2000.0
35:Equinox
31:J2000.0
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1399:13 (x)
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317:SIMBAD
218:Radius
130:+1.21
119:+0.75
1620:M1-67
1608:Other
1509:Other
1308:Bayer
1299:Stars
1211:S2CID
1168:S2CID
1125:S2CID
1099:arXiv
1049:(PDF)
909:S2CID
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809:arXiv
739:S2CID
628:S2CID
602:arXiv
333:is a
28:Epoch
1599:6866
793:Gaia
765:2237
497:The
467:The
338:star
323:data
198:Mass
124:B−V
113:U−B
42:ICRS
1591:NGC
1203:doi
1160:doi
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