Observing Planetary Nebulae

NGC 6543 Cat’s Eye Composite image. X-ray: NASA/UIUC/Y.Chu et al., Optical: NASA/HST

TAAS 101 Jon Schuchardt December 2016 Outline

• What is a ?

•

• Classifying planetary nebulae

• How to find, observe, and report NGC 7027 “Magic Carpet” () Credit: NASA, H. Bond (STScI) What are Planetary Nebulae?

• Nothing to do with planets!

• Many PNs first observed by were disks that responded well to magnification, like planets. E.g., the Nebula (NGC 7009)

• Late evolutionary stage of -like

• Faintly luminous clouds of ionized gas: expelled layers surrounding a left-over NGC 5882 core or “” () Credit: H. Bond, HST, STSci, NASA • Short lifetime: about 10,000

• About 3000 planetary nebulae known in the

Stellar evolution

• The fate of a is mass-dependent

• Massive stars (> 8X mass of the Sun) burn hot and die young and violently in 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 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 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 . 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:

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 “”

• First locate the

• Target is about a third of the way from Altair to

• Can you see , 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 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 Pocket Sky Atlas, p. 63

M57: The

Find , 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 , 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) 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. French, Celestial Sampler 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.

3. 66, 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 The Helix: Comparing Views

Astronomical League Planetary Nebulae Observing Guide, p. 64 The Skull ()

• Best in Dec/Jan

• Use β Ceti and scan N to locate φ1-φ4

From S. French, Celestial Sampler The Skull: NGC 246

Use φ2 and φ1 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 The Skull: Comparing Views N

W

W N

AL Observing Guide, p. 29 Okay, so some imagination is needed! Everyone needs a Crystal Ball: NGC 1514

This one’s 6 degrees NE of the Seven Sisters

From S. French, Celestial Sampler The Crystal Ball:

1. Forms a 345 triangle with Aldebaran and the .

2. Connect the dots from ο to ς Persei ESE to target

3. An “obvious” central star.

4. Can you see your future in the globe? Pocket Sky Atlas, p. 15 The Crystal Ball: Comparing Views

AL Observing Guide, p. 32

Credit: NASA “Ride the River” to Cleopatra’s Eye: NGC 1535

Start at Rigel, and flow W to ο1 and ο2

From S. French, Celestial Sampler Pocket Sky Atlas, p. 17

Cleopatra’s Eye:

1. From ο1 and ο2, head due S to 39 Eridani and then to target.

2. Do you see blue color? Any tilt to the object? Cleopatra’s Eye: Comparing Views

AL Observing Guide, p. 32 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 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 N

W

N AL observing W guide, p. 58 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! 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 Another “stellar” PN IC 4776

1. Forms an almost 345 triangle ε and 5th mag sun to PN’s south.

2. Observe the low power field

3. “Blink” using an OIII filter to identify which star-like object “responds” to the filter. Pocket Sky Atlas, p. 67 PNs also respond to narrowband filters, but an OIII filter is essential for working the AL program. 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 A closer look at NGC 6567 in M24: 1. Locate M24, an easy binocular target.

2. Use the 6-7th magnitude stars at the SW end of M24 to find where to center the crosshairs of your finder.

3. “Blink” the low power field with the OIII filter to find Waldo; only the PN will “respond” to the filter! Pocket Sky Atlas, p. 67 N

Does this look hopeless, W or what!?!

AL observing guide, p. 48 Thar’ she blows!

If you can “blink it,” you can find it, too!

Behold the power of the OIII filter! Confirmed by finding same star AL observing guide, p. 48 pattern in the fingerprint of the “impossible” photo

W

N 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!

Final thoughts

• Planetary nebulae: dying stars with diverse shapes/sizes

• End game of a complex process of stellar evolution NGC 7662 • An observing program within a summer’s The Blue Snowball grasp 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 Thanks for your attention!

The Albuquerque Astronomical Society Observe, Educate, Have Fun

Visit www.taas.org to learn more about what TAAS has to offer!