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The Photometric and Spectral Evolution of the 2008 NGC 300 Transient

The Photometric and Spectral Evolution of the 2008 NGC 300 Transient. Roberta M. Humphreys University of Minnesota. Discovery April 24, 2008 by Monard. Smarts 1.3m BVRIJHK May 15 – Jun 22, 2009 1.5m spectroscopy May 15 - Jan 22, 2009

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The Photometric and Spectral Evolution of the 2008 NGC 300 Transient

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  1. The Photometric and Spectral Evolution of the 2008 NGC 300 Transient Roberta M. Humphreys University of Minnesota Discovery April 24, 2008 by Monard Smarts 1.3m BVRIJHK May 15 – Jun 22, 2009 1.5m spectroscopy May 15 - Jan 22, 2009 Magellan MagE July 6, Aug 30/Sep 1 2008, Jun 05, 2009 The progenitor Prieto 2008from Spitzer 2003, 2007

  2. Basic Properties Pre-eruption IR SED => Lsun = 5.5 x 104 Lsun, Mbol = -7.1 mag Maximum light mv = 14.7 mag => Mv = -12.1 or -12.9 mag, Av = 0.3 or 1.2 Increased luminosity by ~ 100 times or more Spectrum at max, F-type supergaint abs line + H, Ca II, [Ca II] emission Total emitted energy ~ 1047 ergs Mass of progenitor ? 10 – 15 Msun

  3. The Spectral Energy Distribution 7500 K BB, f-f, 715 K dust L* = 1.3 x 107 Lsun R* max = 10AU Rdust = 1750 AU = 10 light days Dust survived the initial eruption observed corrected

  4. Evolution of the Spectrum– the Eruption Berger et al. 2009 Bond et al. 2009 F-type supergiant spectrum expected in an eruption forming optically thick wind At max – complex Ca II profiles, Vel (em and abs) ~ 400 km/s, FWHM of Ha ~ 1000 km/s

  5. Evolution of the Spectrum – Post-Eruption The Double-Peaked Hydrogen and Ca II Emission Lines bipolar/asymmetric outflow – expansion Ca II primary 79 km/s secondary 164 km/s Hydrogen primary 69 km/s secondary ~ 200 km/s

  6. Ca II and [Ca II] Emission The Asymmetric [Ca II] profiles Thomson scattering Auer and Van Blerkom 1972 demonstrated effect of electron scattering on profiles in expanding ejecta for recombination lines -- asymmetric profiles with red wings. Hillier 1991

  7. Other Emission Lines The Absorption Line Spectrum He I 5876 + other weak em 7065, 6678, 3964, 3888 O I 8446 -- Ly b pumping, by flourescence [O I] 6300, 6363 Fe II [Fe II] O I 7774 (lum sensitive ~ -6.9 Mv ) Sr II, Ca I, Mn I, Ti II, V II Ba II : 4554, 4934 Na I D (also O I 8446, Berger et al. ) Double Ca II H and K Expanding envelope becoming transparent to ionizing radiation Rapid transition from absorption to emission Jul 18 (abs)  Sep 08 (em)

  8. Clues from the Velocities Expected Vel galactic rotation 190 km s-1 Max . 15 May Em. and abs. ~ 400 km s-1 Post-eruption -- Double-peaked profiles ( abs min.Ca II and H)  200 +/- 2.7 km s-1 (14) Emission lines (Aug/Sep)  200 +/- 4.4 km s-1 (40) Absorption lines (July)  180 +/- 1.7 km s-1 (33)

  9. Eruption and Post – Eruption Maximum – redshifted vel ~ 400 km/s expansion ~ 500 km/s, Post-eruption – 20 – 30d -- shift to lower vel abs and em lines Initial eruption followed by a dense slowly expanding false photosphere and asymmetrical bipolar outflow Abs lines weaken, transition to em (Na I and O I) 100d dense wind becomes transparent to ionizing radiation

  10. Thoughts on the nature of the N300 Transient and origin of instability Progenitor (IR SED)  a high mass loss state, tip of AGB or supergiant OH/IR star lack of IRAC variability, outflow velocity (75 km s-1)  post AGB/RSG Outflow vel. greater than AGB/RSG, lower S Dor vars. Initial mass -- Lum  10-15Msun, 13-17Msun CMD (Gogarten et al. 2009) PAH feature/ Ba II?  post AGB, proto-PNe, lower initial mass But no carbon bands: CH, CN, C2 Origin of the ionizing radiation

  11. Intermediate-mass post -AGB/RSG on a blue loop

  12. Other members of this sub-group SN2008S SN2010da SN2010dn M85 2006 OT? M31 RV X At Maximum: F-type supergiant spectrum, Ca II and [Ca II] em, dusty progenitors, increased 100 – 1000 times in luminosity

  13. Optically obscured, “cool” transients NGC 300 2008 OT SN2008s SN2010da Prieto 2008 Prieto et al 2008 Khan et al., Berger et al. 2010 T= 350K BB L = 5.5 x 104 Lsun, Mbol = -7.1 mag at maximum Mv = -12.1 or -12.9 mag L = 1.1 x 107 Lsun T= 440K BB L = 3.5 x 104Lsun Mbol = -6.8 mag at maximum Mv = -13.6 mag L = 3 x 107 Lsun T= 890 K BB L = 1.3 x 104 Lsun Mbol = -5.5 mag at maximum Mv = -10.4 mag L = 1.1 x 106 Lsun In “eruption” increased 100 – 1000 times

  14. The spectra SN2010da spectrum H em, [N II], He I, O I, Ca II ? No [Ca II] ! He II 4686 ! ATEL 2637 (Chornock & Berger)

  15. These are not LBVs !

  16. A future meeting -- Outstanding Theoretical Problems in Massive Star Research Minnesota Institute for Astrophysics and Fine Theoretical Physics Institute University of Minnesota October 2012 IMPOSTOR !

  17. A candidate for membership? UGC 2773 2009 OT At max ~ 107 Lsun Increased 22.8 -> 17.5 mR Progenitor -7.8 Mv Color -> ~ A-type 1.3 x 105 Lsun ~ 20Msun (CMD)

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