Transcript Analyzing HII Regions

Discovery and Characterization
of Galactic Ionized Nebulae with
WHAM
Peter Doze, Texas Southern University
Advisor: Dr. Bob Benjamin
University of Wisconsin-Madison
National Astronomy Consortium
Finkbeiner (2003)
The Wisconsin H-alpha Mapper (WHAM)
• Wisconsin H-Alpha Mapper (WHAM)
detects faint optical emission lines from
the diffuse warm interstellar medium.
—One-degree beam
—Velocity baseline of ~200 km/s
—Velocity resolution of 12 km/s
• Much of the sky was observed from Kitt
Peak (Haffner et al 2003); the southern
sky is currently being observed from
Cerro-Tololo observatory .
This is the FIRST velocity resolved all-sky survey of H-alpha emission.
The major goal is to characterize the diffuse ionized gas. I worked on
the properties of the brighter ionized nebulae.
Ionized Nebulae in the “Warm Ionized Medium” (WIM)
1950-1959
1960-1969
To
date
1970-2014
Started off by searching for bubbles/ionized regions in a combined H-alpha image
from Finkbeiner (2003) using data from Southern H-alpha Sky Survey Atlas (SHASSA
Gaustad et al 2001), Virginia Tech Spectral survey (VTSS, Dennison et al 1998) and
WHAM. We had 758 H-alpha nebulae total and 105 new (uncatalogued?) regions.
HII Regions=Ionized Nebulae?
• Regions characterized by Hα
emission
• Photo-ionized by UV or X-ray
photons.
• If UV sources is O or B stars
(T~40,000K), usually called a
“HII region”
• Ionized region=“Strömgren
Sphere”
• H-alpha produced by
“recombination”
Schematic showing Bohr
radius/quantum number of
hydrogen atoms
Analysis of the Identified Bubbles
A test case-The Circinus Bubble
5 degrees diameter
Distance constrained by CO
(molecular) cloud in lower right
absorbing the optical emisison.
Distance to cloud is 435 pc (Knude
2010) and the cloud has active star
formation.
Bubble center is at z=-20 pc (below
midplane)
Bubble radius is 20 pc.
Possible Ionizing sources: HD 135240
(O8.5 V) and HD 135591 (O8 III p)
H-alpha flux consistent with UV
photons expected from these stars.
Diameter of ~5 degrees
Looking at intensity vs. radius
Automating this process for 278 nebulae!
• After practicing with the Circinus HII region, we
made a list of ALL bubbles with at least one
WHAM beam center inside the bubble.
• Created a table of the direction, angular radius,
number of WHAM beams, total intensity, and
average first and second velocity moments.
• With this we were able to calculate the
Galactocentric Radius and the distance from the
Sun
The red figure is a histogram of physical sizes,
calculated with the angular radius and the distances
calculated.
The blue figure is a histogram of the SII/H alpha ratio
and the vertical black line is the average.
The green figure is a histogram of the linewidths of
the HII regions
Map of HII Regions
The Orange dots are known HII regions and the Red dots are the uncategorized HII regions.
Results
We have used the H-alpha compilation image of Finkbeiner (2003) to
create a master catalog of H-alpha bright regions consisting of 738
objects, of which 105 are apparently not cataloged yet.
We examined in detail the distribution of the intensity and first and
second velocity moments for a selected set of bubbles, in particular
the (uncataloged) Circinus bubble.
We have generated a table of kinematic distances, intensites,
velocity moments and (when available) [S II]/H-alpha line ratios for
278 objects with bubbles containing WHAM pointing centers.
Future work: validation of the table results and comparison with
previous velocity measurements when available.
University of Wisconsin-Madison
NAC Lows
There were only two NAC students on site. I
feel that this made it harder to follow the
NAC outline because the majority of students
where regular REU students.
University of Wisconsin-Madison
NAC Highs
The supportive master/apprentice
relationship contributed to my success during
the summer. When I hit a wall (IDL) I could
always quickly access my personal mentor or
the other mentors on site for help.
Another consequence of the NAC’s
mentorship is my visit to Kitt Peak to observe
on the 0.9m telescope. I was able to operate
all aspects of the telescope including tracking,
file management, and filter selection.
Rgal
•
Joachim Köppen Kiel (2014)