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What Are Planetary Nebulae?

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What Are Planetary Nebulae? Observing Planetary Nebulae NGC 6543 Cat’s Eye Nebula Composite image. X-ray: NASA/UIUC/Y.Chu et al., Optical: NASA/HST TAAS Astronomy 101 Jon Schuchardt December 2016 Outline • What is a planetary nebula? • Stellar evolution • Classifying planetary nebulae • How to find, observe, and report NGC 7027 “Magic Carpet” (Cygnus) Credit: NASA, H. Bond (STScI) What are Planetary Nebulae? • Nothing to do with planets! • Many PNs first observed by William Herschel were disks that responded well to magnification, like planets. E.g., the Saturn Nebula (NGC 7009) • Late evolutionary stage of sun-like stars • Faintly luminous clouds of ionized gas: expelled layers surrounding a left-over NGC 5882 core or “white dwarf” (Lupus) Credit: H. Bond, HST, STSci, NASA • Short lifetime: about 10,000 years • About 3000 planetary nebulae known in the Milky Way Stellar evolution • The fate of a star is mass-dependent • Massive stars (> 8X mass of the Sun) burn hot and die young and violently in supernova explosions • Sun-like stars are cooler, live longer, and “fade away” as white dwarfs/planetary nebulae • Stellar evolution is complex • Requires an understanding of atomic and nuclear physics, electromagnetism, thermodynamics, gravitation, and quantum mechanics coupled with rationalization of a vast amount of observational data. • Need for a star to maintain hydrostatic equilibrium requires balance of outward pressure (fusion reactions) and inward pressure (gravity) Stellar evolution simplified: S. Schneider and T. Arney, Pathways to Astronomy (2007), p. 483 A deeper dive . 7->8: Sun-like star leaves the Main Sequence for the Subgiant Branch. Remaining hydrogen is consumed rapidly (hydrogen shell-burning stage) 8->9: Red Giant Branch. Radius increases 100X. Core increases in density & temp while shell expands & cools 9->10: Helium flash, followed by fusion of helium to carbon in the core, fusion of hydrogen in outer shell E. Chaisson and S. McMillan, Astronomy Today, 6th ed. (2008) 10->11: Star returns to the Red Giant Branch (“AGB”). Shrinking, fused carbon core with depleted He and H- burning shells. 11->12: Pulsating He-shell flashes, increasing instability, and ultimate ejection of star’s envelope. Result: A hot, dense carbon core and an expanding cooling cloud of dust the size of our solar system. Burning core’s UV radiation ionizes the cloud to give the “planetary nebula.” 12->13: Hot, dense carbon core of the white dwarf “shines” by stored heat. From E. Chaisson and S. McMillan, Astronomy Today, 6th ed. (2008) Classifying Planetary Nebulae: Vorontsov-Velyaminov System 1. Stellar 2. Smooth disk Morphological System a. Brighter toward center b. Uniform brightness 1. Round c. Traces of ring structure 2. Elliptical 3. Irregular disk 3. Bipolar a. Very irregular brightness distribution 4. Quadrupolar b. Traces of ring structure 5. Point symmetric 4. Ring structure 5. Irregular (similar to a diffuse nebula) 6. Anomalous Astronomical League-- Observing Program • Complete visually or by imaging • Basic level: 60 objects earns a certificate • Advanced level: all 110 objects observed or tried well • Imaging: 90 objects WARNING: Astronomical League observing programs can be highly addictive! Astronomical League--Observing Program • Requirements: • AL League member • Observe 60 or image 90 of 110 objects listed in the AL’s Planetary Nebulae Observing Guide (buy online) • Use any method for locating the PNs (GOTO allowed) • Recognition for all “manual” observing • Negative observations accepted for advanced program only with a sketch and at least two failed efforts • Record date, time, location, sky conditions, equipment used as in other AL programs • Other details needed: check the website or use the template provided Specific added requirements for the AL program: Requirements in addition to the usual date, time, location, conditions: • Filters used, magnifications used. • A detailed description of the object that includes at minimum: • Is the central star visible? • Is a filter required to observe the PN? • How does the PN respond to different magnifications? • Is the object directly visible or does it require averted vision? • A detailed description of the object’s appearance OR a sketch of the object. • Optionally, describe other unique characteristics?: • Colors seen? Blink effects? Shape of object? • Stellar? A disk? A ring? Bipolar? Symmetrical? • Evenly illuminated? Any shells, crowns, or anse seen? Jim K’s Observing Questions for Describing Planetary Nebulae: • Is nebulosity seen with direct vision, or is averted vision needed? • Does it respond strongly or weakly to filters? UHC, O-III, other? • What is the overall shape? Are the outer edges sharp or diffuse? • Does the size or shape change when using averted vision? • Is it uniformly bright or are there any brighter/darker areas? • Are any central or other related stars visible? • Is any color seen in the nebula or nearby stars? • Are other objects of interest in the same field of view? Some fun facts • Only 4 of Messier’s 110 objects are planetary nebulae (M27, M57, M76, M97) • Only 22 additional planetary nebulae are Herschel 400 objects • M76 is on both the Herschel 400 and Messier lists M97: The Owl • Only 9 planetary nebulae are (Ursa Major) Credit: AURA/NOAO/NSF Herschel II objects The basic level of the AL’s Planetary Nebulae program can be completed during a single summer observing season! Another Fun AL Observing Program: Observing Stellar Evolution Minimal requirements to earn a certificate and pin: object name, date, time, location, telescope used, magnification, and a simple object description. • Develop an understanding of the HR diagram • Seen before? Must observe again for this program • 100 objects grouped into 11 categories: • Stellar nurseries (14) • Planetary nebulae (9) • Colorful stars (34) • High-mass stars (6) • Young open clusters (7) • Red supergiants (5) • Main sequence low-mass stars (8) • Supernova remnants (2) • Red giants (6) • Variable stars (4) • Carbon stars (5) Observing Stellar Evolution Easy recordkeeping--use the supplied form or create a simple spreadsheet: Object Con Date Time Site Magn. Category Description μ And And 11/25/2016 6:15 home 85 Colorful stars Mag: 3.9; "A" star. White to pale yellow; bright, naked-eye star. Mag: 7.5; "O" star. White. Other stars in field; part of multi- HD14633 And 11/25/2016 6:25 home 85 Colorful stars star system. NGC Blue "snowball" disk at 85, 170X. Strong blink effect when 7662 And 11/25/2016 6:35 home 85, 170 Planetary nebula viewed directly. Circular and dense; an obvious PLN. Gliese 67 And 11/25/2016 6:45 home 85 Low-mass stars Mag: 5; "G" star, 0.97 sm. White to pale yellow, brilliant. NGC Cat's Eye is blue, slightly oval at edges, tilting N-S. Good blink to 6543 Dra 11/25/2016 6:55 home 85, 170 Planetary nebula disappear effect at 85, 170X. Mag: 2.1; "B" star, eclipsing binary. Brilliant white, est. mag: 3 Algol Per 11/25/2016 7:00 home 85 Colorful stars (2.1-3.4 range) Mag: 4.9; "O" star, 16 sm. White, bright. A 9th mag companion 10 Lac Lac 11/25/2016 7:10 home 85 High-mass star is close to NE. σ Dra Dra 11/25/2016 7:15 home 85 Low-mass stars Mag: 4.7; "K" star, 0.82 sm. Pretty, bright, yellow. β And And 11/25/2016 7:20 home 85 Red giant Mag: 2.1. Brilliant yellow-orange. Easy naked eye star. Mag: 2.0; "F" star. Brilliant white primary with 8-9th mag blue Polaris UMi 11/25/2016 7:25 home 85, 170 Colorful stars companion to its lower right. Spectacularly rich and bright side-by-side open clusters, each Double Young open with high central concentration and countless resolved suns. cluster Per 11/25/2016 7:30 home 56 clusters Pair of fried eggs at 9X. Sugar on velvet at 56X. Oriented E-W. “Observing is something you do with your mind. It’s not about simply seeing the object. It’s about understanding what the object is, why it is important, why it is interesting, and how it fits into the story.” -- --Bill Pellerin, AL program coordinator Helpful references for observers new & old: Eskimo nebula Spring Sky Finder chart for Messier objects. Star Watch, Philip S. Harrington Sorry, my battery died . Photo by Phil Fleming . But we don’t need no stinkin’ hand controller! Let’s find M27: • The “Dumbbell Nebula” • First locate the Summer Triangle • Target is about a third of the way from Altair to Deneb • Can you see Sagitta, the Arrow? From S. French, Celestial Sampler Pocket Sky Atlas, p. 64 To the atlas! • Scan north from Altair to find the 4 bright stars of Sagitta • Follow the arrow to γ Sagittae • Scan due N to “M” shape of 5th/6th magnitude suns • Center the crosshairs of the finder just S of the center point of the “M” A closer look at M27 and the “M”: • All stars of the “M” fit nicely in a finderscope view or within a binocular view • M27 is visible in binoculars as a faint smudge: can you see it? • Eye candy at low to medium power in the telescope • Enjoy unfiltered! Pocket Sky Atlas, p. 64 NASA/JPL-Caltech/J. Hora (Harvard-Smithsonian CfA) - JPL Viewer discretion is advised: Your view of M27 may not match that of the Spitzer Space Telescope Pocket Sky Atlas, p. 63 M57: The Ring Nebula Find Vega, brightest star in the Summer Triangle Lyra, the Lyre, has a diamond of 4th-5th magnitude stars pointing SE of Vega M57 is on the line between λ and β Lyrae M57: The Ring Nebula If I could just borrow the Hubble Space Telescope, I’d have this view! Hubble Heritage Team (AURA/STScI/NASA) What should I expect to see through a backyard telescope? Think “black-and-white,” baby! Planetary nebulae are diverse: • The large and the obvious (the Dumbbell: M27) • The even larger but less obvious (the Helix: NGC 7293) The Skull Nebula • The irregular (the Skull: NGC 246; the Fetus: NGC (above) and the 7008) Helix Nebula Spitzer Space Telescope • The compact and the obvious (the Ring: M57 and NASA/JPL the Cat’s Eye: NGC 6543) • The colorful (the Magic Carpet: NGC 7027; the Blue Snowball: NGC 7662) • Stellar planetaries (NGC 6886, NGC 6567) Finding the Helix • Best in Oct/Nov, but still in Dec sky • Use β Ceti and Fomalhaut to locate δ and τ Aquarii From S.
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