Endpoints of Stellar Evolution Neda Hejazi April 2017

Endpoints of Stellar Evolution Neda Hejazi April, 2017

Proto-PNe and PNe Ø PPNe: Post AGB stars ✪ Intermediate-mass stars evolved from AGB ✪ Ejecting shell of gas and dust ✪ Mass loss and core contraction Ø CSPNe: Central stars of PNe Spectra: ✪ Subdwarf O-type stars ✪ Wolf-Rayet stars (WO, WC) ✪ Very hot proto-white dwarfs WHITE DWARF STARS Red Rectangle (HD 44179)

WD: The most common Endpoint of Stellar Evolution

Historical Notes on WD Ø Friedrich Bessell (1844) ✺ Proper motion of Sirius and Procyon wobble ✺ Suggested they orbited “dark stars” Ø Alvan Clark (1862) ✺ Discovered Sirius B ✺ Northwestern’s Dearborn Observatory Ø John M. Schaeberle (1896) ✺ Discovered Procyon B ✺ Lick Observatory

Historical Notes on WD •

Historical Notes Ø First WD systematic classification by G. Kuiper in 1941 ✰ Prefix “w” for signifying a WD ✰ “A type” : hydrogen lines ✰ “F type”: Ca II lines ✰ “G type”: weaker metallic blends ✰ “Con type”: featureless spectrum Ø Luyten 1952 ✰ Changing prefix “w” to “D” ✰ “B type”: only He I ✰ Adding a numeric subtype to indicate temperature

Historical Notes •

Current Classification Updated version from Mc. Cook & Sion 1999 D: degenerate star A, B, C, O, Z or Q: Primary spectroscopic characteristic

Current Classification •

Current Classification: DA Broad Balmer lines become sharper and weaker, as Teff decreases, almost disappearing around DA 10

Current Classification: DB

Current Classification: DZ Prominent Ca II H & K lines weaken as Teff decreases

Current Classification Ø Surface gravity Index: Early indicators of the line widths: ✾“d” for diffuse due to high gravity ✾“n” for narrow or “s” for sharp due to low gravity Recent numeric indicators: Example: DB 1. 3_ 7. 9 ✾A WD with a temperature of about 38, 800 K and a log g of 7. 9 ✾Further refinement half-integer indices for temperature Ø “Dusty DAZ” WD ✾IR excess ✾Photospheric Balmer lines and metal lines surrounded by dusty disk DAZd ( “d”: circumstellar dust)

Why WDs in UV? •

A comprehensive NUV and FUV study of the Hot DA WD G 191 -B 2 B by FUSE Preval et al. 2013

A comprehensive NUV and FUV study of the Hot DA WD G 191 -B 2 B by HST/STIS Preval et al. 2013

A comprehensive NUV and FUV study of the Hot DA WD G 191 -B 2 B by HST/STIS and FUSE Ø Preval et al. 2013 Ø https: //archive. stsci. edu/prepds/wd-linelist/

Cataclysmic Variables Interacting Binaries •

Cataclysmic Variables Interacting Binaries Ø Helium CVs: mass transfer of helium-rich material to WD instead of hydrogen-rich material Ø Polar variables: with strong magnetic field, accretion disk does not form, funneling the accreted mass onto a spot (a magnetic pole) on the surface of the WD, WD spin is synchronized with the orbital period of accreting material Ø Intermediate polars: weaker magnetic field, forming a partial accretion disk, WD spinning more rapidly than the orbital period of the disk

Novae Ø Nova explosion observed as a sudden brightness, followed by a decline Classical Novae: Having only one recorded outburst Recurrent Novae: Having more than one nova outburst Recurrence period: a few years to a few decades Ø Extending the monitoring time to hundreds or thousands of years All novae would be seen to erupt over and over!

Classical Novae •

Novae

Novae

Novae: Model •

May Become Dwarf Nova: Disk Instability Ø Causing regular, low amplitude bright phases Ø Termed: dwarf nova outbursts Ø Example: SS Cyg ✤ Going through a CV-type outburst ✤ Brightening the system from V=12 to V=8 The data from the American Association of Variable Star Observer (AAVSO)

Novae: Accreted Envelope • Increasing T Temperature rise gets out of control Thermo Nuclear Runaway (TNR)

Novae: Expanding Shell •

Novae: Remaining Accreted Material •

Novae: Speed Classification Ø Classified depending on the time taken to decline by two magnitudes from outburst maximum: “t 2” ØVery fast: t 2 < 10 days Ø Fast: t 2 = 11 -25 days Ø Moderately fast: t 2= 26 -80 days ØSlow: t 2= 81 -150 days ØVery slow: t 2= 150 -250 days Smooth light curves Irregular light curves

Novae: Speed Classification Featureless light curve of a fast nova Irregular light curve of a slow nova

Nova: Outburst Spectrum Ø Clear signature of a TNR and an expanding material Ø The evolution of the photosphere, wind and surface nuclear reactions Ø Dominated by permitted, recombination lines during the initial stages: low-ionization levels Ø Increasing ionization level with time Layers closer to the ionizing source (central WD) revealed as the ejecta expands Ø Forbidden lines at later stages: high-ionization levels Ø Decreasing ionization level in post-outburst quiescence phase

Nova: Spectral Classification Ø Old classification system: Mc. Laughlin 1960 ✽ Pre-maximum ✽ Principal ✽ Diffuse enhanced ✽ Orion ✽ Nubular ✽ Post nova ØA more versatile classification system: Williams et al. 1991; 1994 ✽ Based on the Cerro Tololo Nova Survey from 1987 to 1994 ✽ aka: “Tololo Nova Spectral Classification System” ✽ Concentrating on post-outburst spectra ✽ No Spectra at maximum light were obtained in the Tololo system

Nova: Photographic Spectra at Maximum Payne-Gaposchkin 1957 and Mc. Laughlin 1960 Ø Example: V 603 Aql, DQ Her and Nova Pictoris Ø Having absorption lines resembled A or F supergiants: Interesting! Ø Williams et al. 1991: ★ Is the max-light spectrum a purely absorption spectrum? ★ Weak emission lines might have suppressed in photographic spectra! ★ Their spectra show emission features shortly after max light

• Nova: Tololo Spectral Classification Early Phase

Nova: Tololo Spectral Classification Evolutionary Phases •

Nova: Tololo Spectral Classification Phases: Subclasses Phase C: Coronal Subscript Phase P: Permitted Phase A: Auroral Phase N: Nebular Superscript

Cen 1991: Fe IIn Nova

Sgr 1991: He/N Nova

V 2362 Cygni: Fe II nova

V 2491 Cygni: He/N nova

Other CVs: Recurrent and Dwarf Novae Looking like an M-giant with superimposed Balmer emission lines Emission Spectrum Absorption Spectrum Recurrent nova at quiescence Dwarf nova during outburst

Supernovae •

Supernovae: Classification • Early times ✿ Type Ia: a complex of Fe and Co emission lines due to forbidden transitions indicating SNe have entered the nebular phase ✿ Type Ib and Ic : Dominated by strong emission features due to elements: C I, O I, Mg I, Na I and Ca II ✿ Type Ib and Ic : difficult to distinguish as He I lines in Ib fade with time

Supernovae: Classification Subtypes For Type II Based on appearance in the light curve Ø IIL: a single maximum followed by a fairly steep but linear (L) decline, less deep after 100 days but still linear Ø IIP: a distinct plateau (P) shortly after the maximum, 1 mag below maximum, followed by a short, steep decline before a shallower linear decline Based on spectral diversity Ø IIn: Typical early-time Type characterized by broad lines, but a subset show much narrower lines (n) Ø IIb: Spectra evolving to resemble those of type Ib, having strong hydrogen lines at early times that are relatively weak at later times, implying a thin Hydrogen envelope

Supernovae: Classification

Supernovae: Classification Early Times

Supernovae: Classification Late Times

Supernovae: Classification Subtypes For Type II