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

Basic Properties Pre-eruption IR SED => L sun = 5.5 x 10 4 L sun, Mbol = -7.1 mag Maximum light m v = 14.7 mag => M v = or mag, A v = 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 ~ ergs Mass of progenitor ? 10 – 15 M sun

The Spectral Energy Distribution 7500 K BB, f-f, 715 K dust R * max = 10AU R dust = 1750 AU = 10 light days Dust survived the initial eruption L * = 1.3 x 10 7 L sun observed corrected

Evolution of the Spectrum – the Eruption Berger et al. 2009Bond et al 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 H  ~ 1000 km/s

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 Evolution of the Spectrum – Post-Eruption

Ca II and [Ca II] Emission The Asymmetric [Ca II] profilesThomson 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

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

Clues from the Velocities 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) Expected Vel galactic rotation 190 km s -1

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

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, C 2 Origin of the ionizing radiation

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

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

NGC OT SN2008s SN2010da Optically obscured, “cool” transients Prieto 2008Prieto et al 2008Khan et al., Berger et al T= 350K BB L = 5.5 x 10 4 L sun, Mbol = -7.1 mag at maximum Mv = or mag L = 1.1 x 10 7 L sun T= 440K BB L = 3.5 x 10 4 L sun Mbol = -6.8 mag at maximum Mv = mag L = 3 x 10 7 L sun T= 890 K BB L = 1.3 x 10 4 L sun Mbol = -5.5 mag at maximum Mv = mag L = 1.1 x 10 6 L sun In “eruption” increased 100 – 1000 times

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

These are not LBVs !

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

A candidate for membership? UGC OT At max ~ 10 7 L sun Increased > 17.5 m R Progenitor -7.8 Mv Color -> ~ A-type 1.3 x 10 5 L sun ~ 20M sun (CMD)