Observing Planetary Nebulae

Transcription

1 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

2 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)

3 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 NGC 5882 (Lupus) Credit: H. Bond, HST, STSci, NASA Faintly luminous clouds of ionized gas: expelled layers surrounding a left-over core or white dwarf Short lifetime: about 10,000 years About 3000 planetary nebulae known in the Milky Way

4 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)

5 Stellar evolution simplified: S. Schneider and T. Arney, Pathways to Astronomy (2007), p. 483

6 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, 6 th ed. (2008)

7 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, 6 th ed. (2008)

8 Classifying Planetary Nebulae: Vorontsov-Velyaminov System 1. Stellar 2. Smooth disk a. Brighter toward center b. Uniform brightness c. Traces of ring structure 3. Irregular disk a. Very irregular brightness distribution b. Traces of ring structure 4. Ring structure Morphological System 1. Round 2. Elliptical 3. Bipolar 4. Quadrupolar 5. Point symmetric 5. Irregular (similar to a diffuse nebula) 6. Anomalous

9 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!

10 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

11 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?

12 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?

13 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 Only 9 planetary nebulae are Herschel II objects M97: The Owl (Ursa Major) Credit: AURA/NOAO/NSF The basic level of the AL s Planetary Nebulae program can be completed during a single summer observing season!

14 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) Colorful stars (34) Young open clusters (7) Main sequence low-mass stars (8) Red giants (6) Carbon stars (5) Planetary nebulae (9) High-mass stars (6) Red supergiants (5) Supernova remnants (2) Variable stars (4)

15 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 multistar HD14633 And 11/25/2016 6:25 home 85 Colorful stars 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. Algol Per 11/25/2016 7:00 home 85 Colorful stars Mag: 2.1; "B" star, eclipsing binary. Brilliant white, est. mag: 3 ( range) 10 Lac Lac 11/25/2016 7:10 home 85 High-mass star Mag: 4.9; "O" star, 16 sm. White, bright. A 9th mag companion 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. Double Young open Spectacularly rich and bright side-by-side open clusters, each 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

16 Helpful references for observers new & old:

17 Eskimo nebula Spring Sky Finder chart for Messier objects. Star Watch, Philip S. Harrington

18 Sorry, my battery died... Photo by Phil Fleming... But we don t need no stinkin hand controller!

19 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

20 To the atlas! Pocket Sky Atlas, p. 64 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 5 th /6 th magnitude suns Center the crosshairs of the finder just S of the center point of the M

21 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

22 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

23 Pocket Sky Atlas, p. 63 M57: The Ring Nebula Find Vega, brightest star in the Summer Triangle Lyra, the Lyre, has a diamond of 4 th -5 th magnitude stars pointing SE of Vega M57 is on the line between λ and β Lyrae

24 M57: The Ring Nebula If I could just borrow the Hubble Space Telescope, I d have this view! Hubble Heritage Team (AURA/STScI/NASA)

25 What should I expect to see through a backyard telescope? Think black-and-white, baby!

26 Planetary nebulae are diverse: The large and the obvious (the Dumbbell: M27) The even larger but less obvious (the Helix: NGC 7293) The irregular (the Skull: NGC 246; the Fetus: NGC 7008) The compact and the obvious (the Ring: M57 and the Cat s Eye: NGC 6543) The Skull Nebula (above) and the Helix Nebula Spitzer Space Telescope NASA/JPL The colorful (the Magic Carpet: NGC 7027; the Blue Snowball: NGC 7662) Stellar planetaries (NGC 6886, NGC 6567)

27 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. French, Celestial Sampler

28 The Helix 1. From δ and τ, scan a finder SW to locate 66, 68, and ν. 2. The Helix is < 1 degree W of ν , 68, ν, and the Helix fit in the 4 degree finder view, but you probably won t see the Helix without the telescope. 4. Use low power! Pocket Sky Atlas, p. 76

29 The Helix: Comparing Views Astronomical League Planetary Nebulae Observing Guide, p. 64

30 The Skull (Cetus) Best in Dec/Jan Use β Ceti and scan N to locate φ 1 -φ 4 From S. French, Celestial Sampler

31 The Skull: NGC 246 Use φ 2 and φ 1 to triangulate to the target. As usual, start with low power. Can you see the outline of the skull? Eyes? Pocket Sky Atlas, p. 7

32 The Skull: Comparing Views N W W N Okay, so some imagination is needed! AL Observing Guide, p. 29

33 Everyone needs a Crystal Ball: NGC 1514 This one s 6 degrees NE of the Seven Sisters From S. French, Celestial Sampler

34 The Crystal Ball: 1. Forms a 345 triangle with Aldebaran and the Pleiades. 2. Connect the dots from ο to ς Persei ESE to target 3. An obvious central star. Pocket Sky Atlas, p Can you see your future in the globe?

35 The Crystal Ball: Comparing Views AL Observing Guide, p. 32 Credit: NASA

36 Ride the River to Cleopatra s Eye: NGC 1535 Start at Rigel, and flow W to ο 1 and ο 2 From S. French, Celestial Sampler

37 Pocket Sky Atlas, p. 17 Cleopatra s Eye: 1. From ο 1 and ο 2, head due S to 39 Eridani and then to target. 2. Do you see blue color? Any tilt to the object?

38 Cleopatra s Eye: Comparing Views AL Observing Guide, p. 32

39 The Epiphany: When you realize why you spent $75 on an OIII filter 1. You were expecting something magnificent, like nearby M27? Guess again! 2. Connect the dots from γ to η Sagittae then E to target. 3. Many bright stars in the low-power view. 4. Which one s the PN? Pocket Sky Atlas, p. 64

40 The Epiphany, cont.: NGC 6886 The AL observing guide shows our quarry at the NW corner of a tiny triangle of stars. AL observing guide, p. 58

41 N W W N AL observing guide, p. 58

42 The blink technique vs. the blink effect The blink technique: Blink the OIII or narrowband filter by passing in front of the eyepiece multiple times as you look through. One object will remain bright while the others dim. No need for a filter wheel. Avoid background light that will reflect off the filter into your eye. Use a headcover if helpful. The blink effect: Blinking can also refer to the way the disk of a PN can seem to disappear when viewed directly versus indirectly. A different concept!

43 Identifying another stellar PN: IC 4776 Stellar PNs are often easy to see but hard to identify without a filter, esp. an OIII filter. Pocket Sky Atlas, p. 67

44 Another stellar PN IC Forms an almost 345 triangle ε and 5 th mag sun to PN s south. 2. Observe the low power field Pocket Sky Atlas, p Blink using an OIII filter to identify which star-like object responds to the filter.

45 PNs also respond to narrowband filters, but an OIII filter is essential for working the AL program.

46 Forensic Astronomy: Where s Waldo? Or: How do I find a stellar PN (NGC 6567) within the Sagittarius Star Cloud (M24)? Pocket Sky Atlas, p. 67

47 A closer look at NGC 6567 in M24: 1. Locate M24, an easy binocular target. 2. Use the 6-7 th magnitude stars at the SW end of M24 to find where to center the crosshairs of your finder. Pocket Sky Atlas, p Blink the low power field with the OIII filter to find Waldo; only the PN will respond to the filter!

48 N W Does this look hopeless, or what!?! AL observing guide, p. 48

49 Thar she blows! If you can blink it, you can find it, too! Behold the power of the OIII filter!

50 Confirmed by finding same star pattern in the fingerprint of the impossible photo AL observing guide, p. 48 W N

51 Take-home lessons Observe the larger, low-surface brightness PNs at low power For others, increase the power to look for a disk, shape, added details that may not be visible at lower magnification A perfect night is not needed; many PNs can be observed with substantial moonlight or local light pollution. Blink with narrowband and OIII filters to identify planetary nebulae, especially stellar ones Look for star patterns in the AL guide photos, but don t let the photos discourage you Some photos are overexposed or are poor copies The blink is your secret weapon If I can tag 60 PNs, so can you!

52 Final thoughts Planetary nebulae: dying stars with diverse shapes/sizes End game of a complex process of stellar evolution An observing program within a summer s grasp NGC 7662 The Blue Snowball Credit: HST/NASA/ESA Don t expect to see a magazine cover Try different magnifications Blink to identify the hidden gem Star-hop your way to discovering these wonderful objects NGC 2392 The Eskimo Nebula Credit: NASA/ESA/STScI

53 Thanks for your attention! The Albuquerque Astronomical Society Observe, Educate, Have Fun Visit to learn more about what TAAS has to offer!