At the Heart of the Matter:The Blue White Dwarf in M 57.

byPaul Temple

A Personal History

• Celestron 6” Refractor

• AS-GT Mount

• SBIG ST-7E (on loan from the AAVSO)

• Cool target of M57

• Began to wonder about the central star

• Cascade effect!

Beauty and the Beast!

SBIG ST-7E, Galileo Filter Wheel and Flip Mirror System

The Image that Started it All!

An Object of Interest!

• In “Burnham’s Celestial Guide” central star is listed as a possible variable.

• The USNO lists it as a star with a 14.20 to 16.40 variablity.

• NSV lists it as being variable as well.

• SIMBAD only gives info on the nebula

Cartes du Ciel

Planetary NebulaM 57 NGC 6720

Constellation: LyraDimension: 1.4'x 1.0'

Magnitude: 9.40 Surface Brightness: 9.30

Description: Ring neb,B,pL,cE Ring Nebula,central* var 14 to 16 mag,PK63+13.1

Round up the the Usual Suspects!

• Arne Henden AAVSO• Arlo Landolt Louisiana State University

• Marc Buie Lowell Observatory

• Tom Kracji Astrokolkhoz Observatory

• Rik Hill Catalina Sky survey

Celestron 6” Refractor Not Adequate!

• Did not have the time or expertise to do a credible job with the 6”

• The Sloan Z (On loan from the AAVSO) filter needed much more aperture than what I had.

• V Would work but just barely!

• Step in the AAVSO!

Handed Off!

• Wrote up observing process

• Submitted it on the Blue/Gold site

• Was accepted and given to Tom Krajci

The Most Interesting Man in the world

Tom KrajciTom Krajci, Major, USAF (retired), is an amateur scientist specializing in photometry. He operates the Astrokolkhoz Observatory at an elevation of 9,440 feet near Cloudcroft, New Mexico. Tom is translating several books on telescope making and optics design from Russian into English, including the works of Dmitry Maksutov.

Wright 28 Telescope

Specs for the Wright 28 Telescope

W28 (Wright-28) is a 28-cm Celestron C-11 located at the Astrokolkhoz telescope facility near Cloudcroft, New Mexico (UT-7). This telescope was donated to the AAVSO by the late Paul Wright.

         Camera: SBIG ST7

         FOV: 14' x 9'

         Pixel scale: 1.08 arcsec/pixel

         Filters: 10-position filter wheel, with Johnson-Cousins BVRcIc, clear filter, Sloan gr, H-alpha (line), H-alpha (continuum, R645), and [SII] (line)

What is a Blue white Dwarf?

• Blue because it is hot!

• 100,000 kelvins

• Dwarf because it has similar mass to the Sun but the size of the Earth

• Degenerate!

• Spins very fast!

• What the Sun will become some day!

Heavy!

To say that white dwarfs are strange is an understatement. An earth-sized white dwarf has a density of 1 x 109 kg/m3. In comparison, the earth itself has an average density of only 5.4 x 103 kg/m3. That means a white dwarf is 200,000 times as dense!

Or what that really means is…

A teaspoonful of typical white dwarf matter would weigh 5.5 tons on Earth - as much as an elephant!

Or…

HOT WHITE DWARFS

DA Objects with atmospheres rich in H, with only traces of He and other elements. This class contains stars encompassing a broad temperature range, from around 6,000K to over 80,000K.

DO He rich objects with temperatures in excess of 45,000K. The spectrum is dominated by the signature of HeII, although H and higher elements may be observed in smaller amounts.

DB This class may be regarded as an extension of the DO group into lower temperature regions (below around 30,000K). The cooler temperatures are insufficient to ionise helium, and so the spectrum is dominated by He I, with only trace amounts of H (only 1/10000th of the observed He abundance).

Table 1.1: Principal white dwarf classes as defined by Sion et al. (1983).

COOL WHITE DWARFS (Temperatures less than 11,000K)

DQ Stars with predominantly He atmospheres, showing lines of molecular or atomic carbon in any part of the spectrum. These stars are cool enough so that H atoms can join together into molecules, and so the signature of molecular H may also be observed.

DZ Stars exhibiting only metal lines from species such as Ca and Fe. No H or He present.

DC Stars showing relatively featureless spectra, because the temperatures are insufficient to excite the atomic H and He into a state where they produce emission/absorption.

Table 1.1: Principal white dwarf classes as defined by Sion et al. (1983).

What is expected• A 3% percent variability

• Around .4 magnitude

• Variability should be in minutes or even seconds

• Unpredictable predictability.

• The thin Hydrogen or Helium atmosphere causes an uneven flickering.

Problems

• PI Photometrically challenged!

• Fairly long exposures

• V and I filters

• Nebulous material interferes with photometry

• Lyra headed below the horizon soon

• Star just dim

• No good spectra and no good way to get it!

How was it done?

• Used AIP4Win v1.4.25

• All images Calibrated with flats, darks and bias frames

• Differential Photometry was used.

• Settings: Star Diaphragm 6

Inner Annulus 6

Outer Annulus 7

Arne Henden’s Fields of Magnitude!

V Magnitude of 11500 NSV

15.85

15.9

15.95

16

16.05

16.1

16.15

1 2 3 4 5

Time

Mag

nitu

de

Magnitude

Each plot is a 1.8 minute exposure exactly 2.2 minutes apart

Time V-C mag K-C mag Magnitude1:32:51 1.428 0.662 16.1211:36:12 1.272 0.63 15.9721:39:32 1.299 0.607 15.9991:42:52 1.41 0.633 16.111:46:13 1.376 0.611 16.076

V images TableV images Table

I Time Series

Magnitude

1515.5

1616.5

1717.5

1818.5

19

1 5 9 13 17 21 25 29 33 37 41 45 49 53

Time 90 second exposures, with a total of 1.8 minutes between.

Mag

nit

ud

e

Magnitude

What was found?

• 11% variability (a full 2 magnitudes!)

• Larger swings confirmed, especially in I

• Minutes scale variability

• Really interesting Object!

What Does this Mean?

• This much magnitude variation is not in any current models.

• Might be a close binary system with Hydrogen loss from one to the other

• Extra hydrogen causes some fusion flickering.

• Unknown process.

For the Future

• Further Time series in UVBRI

• Longer I series

• Time series from other PN’s

• Obtain low resolution spectra of BWD’s

• Write it all up in the JAAVSO

Helix Nebula