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

At the Heart of the Matter:
The Blue White Dwarf in M 57.
by
Paul 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 Nebula
M 57
NGC 6720
Constellation: Lyra
Dimension:
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
Arlo Landolt
Marc Buie
Tom Kracji
Rik Hill
AAVSO
Louisiana State University
Lowell Observatory
Astrokolkhoz Observatory
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 Krajci
Tom 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 JohnsonCousins BVRcIc, clear filter, Sloan gr, H-alpha (line), Halpha (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
16.15
Magnitude
16.1
16.05
16
Magnitude
15.95
15.9
15.85
1
2
3
4
5
Time
Each plot is a 1.8 minute exposure exactly 2.2 minutes apart
V images Table
V images Table
Time
V-C mag K-C mag Magnitude
1:32:51 1.428 0.662 16.121
1:36:12 1.272
0.63 15.972
1:39:32 1.299 0.607 15.999
1:42:52
1.41 0.633 16.11
1:46:13 1.376 0.611 16.076
I Time Series
19
18.5
18
17.5
17
16.5
16
15.5
15
Time 90 second exposures, with a total of 1.8 minutes
between.
53
49
45
41
37
33
29
25
21
17
13
9
5
Magnitude
1
Magnitude
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