FG Sge and PK 60-07.1 history:

• Coordinates (2000.0) = RA : 20h11m55.77s - Dec : +20°18'56.7".
• Informations: m=16.00 - Sbr=24 - Dim: 40.0 x 40.0 " - PA: 90 - Class:3(2).
• The supergiant star FG Sge, is the nucleus of the faint planetary nebula PK 60-7°1. The central star FG Sge is unique as an extremely rapidly evolving post-AGB star with a late Helium flash on its way to the white dwarf stage. On first glance, FG Sge looked rather ordinary. It was recognized as a variable star only recently in 1943, even though it was first photographed in 1894. In 1894 the star was at photographic magnitude +13.6, in 1950 it reached +11, and by 1960 it has surpassed +10. FG Sge continued to brighten and peaked in 1968 around m = +9.5. Between August 1992 and September 1992 a dramatic decline from m= +9.3 to +12.87 was observed. Within these large increases in brightness were small irregular variations. As it turns out, FG Sge has been in constant evolution since the beginning of this century.
• In order to figure out what's happening with FG Sge, it was modeled by the famed astrophysicist Icko lben, Jr. and Mariao Livio in 1992. They concluded that:

  1. FG Sge underwent a helium flash a few centuries in the past, ejecting a shell.

  2. It became a hot star after it ceased hydrogen burning, now burning helium at the core.

  3. Next, hydrogen is ignited in the outer layers of the star.

  4. As the star rapidly evolves to the red end of the spectrum, hydrogen burning mixed with helium burning causes the s-process elements to appear near the surface.

  5. Ejection of a shell caused deeper layers of the star to be observed making it to appear fainter-in the visual and appear bluer. This makes an increase in the ultraviolet (UV) flux.

• Woodward et al. (1993) attributed the first abrupt visual light decline of FG Sge to the formation of a visually optically thick dust shell with a mass of ≃3.3 × ${10}^{-9}$ M⊙ condensed from a shell of gas ejected from the central star. An inspection of the visual light curve reveals that FG Sge has been undergoing irregular, large-amplitude oscillations that vary between ≈200 and 400 days in length since the first dust formation episode. Since the initial visual brightness decline and slow recovery of 1992–1993, a number of such visual brightness drop and recovery episodes have occurred that have been attributed by Gonzalez et al. (1998) to ejections of discrete dust shells similar to those implicated in the R CrB phenomenon. Infrequent observations of FG Sge in the IR have been performed in the early 1970s and 1980s (Tatarnikov et al. 1998). Before the dust shell ejections, the near-IR magnitudes were consistent with the SED of a reddened photosphere surrounded by a dust cloud with a mass of ${10}^{-10}$ M⊙ (Arkhipova & Taranova 1990; Montesinos et al. 1990). However, IR observations of FG Sge at wavelengths longer than 5 μm have been rare. These observations are crucial in the study of the recent activities of FG Sge, because thermal emission from dust will have an SED that peaks at these longer wavelengths (Woodward et al. 1993).

Purpose and dedicated setup:

• Follow all emission lines and lines shape modifications within time.
• Observations setup:
  • Place: OVA (Observatoire du Val de l'Arc), Bouches du Rhône, France.
  • Observer: B. Mauclaire.
  • Hardware: SCT 12" (0.305 mètres)+spectroscope Lhires3 150 traits/mm (2.2 Å/pixel)+CCD KAF-3200ME.
  • Software: acquisition AudeLA, spectral reduction and analysis with SpcAudace (AudeLA's spectral module).

PK 60-07.1 spectrum:

FG Sge 2D spectrum. Geometric corrections done. Note light pollution from urban lights.

PK 60-07.1 normalized spectrum from 4500 to 8300 Å taken August 31th 2010. pk_60-071_20100831_975.fit.

With this mag 16.0 nebula, 2x2 binning and a minimum exposure of 1h20 were required with my SCT 12" and Lhires3 150 g/mm, 27 μm slit spectrograph. Though, with longer exposure, it would have been brighter.
This spectrum shows that such spectrograph as Lhires3 150 g/mm (LISA will do it too) is able to manage faint (mag. 16 !) unstellar targets like this planetary nebula.

15 s exposure on CCD KAF 400. Note the annular PN shape with a mag. 13 surimpressed are visible on right side of the slit.

Chemical analysis:

• Global lines recognition:
  No [OIII] lines visible. A strong [NII] 6543.4 Å line is visible. He 1-5 is a young PN.
  
• Nitrogen lines around Hα:
  
  [NII] emission lines are clearly visible in this low resolution spectrum.
  

FG Sge bibliography:

• C.S. Jeffery, D. Schoenberner, 2006: Stellar archaeology: the evolving spectrum of FG Sge, A&A.
• Croswell, K., 1983, FG Sagittae: One Piece of the Puzzle, Astronomy, October 1983 p 74.
• Hinkle, K., Joyce, R., 1995, Circumstellar CO in FG Sagittae, Astronomical Journal, 109, p. 808-811.
• Iben, I., Livio, M., 1993, A Model for the Dramatic Decline of FG Sagittae, Astrophysical Journal, 406, L15-L16.
• Kipper, T., Kipper, M., Klochkova, V., 1995, The Spectrum of FG Sge in 1994, Astronomy and Astrophysics, 297, L33-L36.
• Mayor, M., Acker, A., 1980, Radial Velocity Curve, and Radius of the Pulsating Star FG Sge, Astronomy and Astrophysics, 92, p. 1-5.
• Van Genderen, A., Gautschy, A., 1995, Deductions from the Reconstructed Evolutionary and Pulsational History of FG Sagittae, Astronomy snd Astrophysics, 294, p. 453-468.
• Van Genderen, A., 1994, On the Pre-Decline and Decline Phases of FG Sagittae, the Post-AGB Star and Central Star of the Planetary Nebula PK 60 -7°.1, Astronomy and Astrophysics, 284, p. 465-476.

PK 60-07.1 bibliography:

• Richard's Astronomy Pages
• Ciel extrême n°6, p25.
• Robert D. Gehrz ,1 Charles E. Woodward: The Development of a Steady State, Asymptotic Giant Branch Type, Circumstellar Wind around the "Born Again" Star FG Sagittae, The Astrophysical Journal, 623:1105-1114, 2005 April 20.