Harvard-Smithsonian Center for Astrophysics Eric's Cool Astronomy Plots
I love to make plots. How often they get published is another matter.
Here are a few of my favorites, some of which might even be useful.
Distance (parsecs) vs. age (in billions of years; Gyr) for the nearest 100 solar-type dwarf stars. Plot made from data in Table 13 of Mamajek & Hillenbrand (2008). The ages were inferred from chromospheric activity levels from the F7-K2 main sequence stars, using the revised rotation vs. age and rotation vs. activity calibrations from this paper. You can think of this as the distribution of ages of the nearest (potential) planetary systems to the Sun, for the nearest Sun-like stars in our Galactic neighborhood.
Pre-MS contraction time versus stellar mass: How long does
it take a pre-main sequence star to contract and reach the zero-age main sequence? It takes
a 1 solar mass star roughly 44 million years to contract to the point at which hydrogen fusion stabilizes
(reaches the main sequence). Plot was contructed using
the D'Antona & Mazzitelli evolutionary tracks.
Cumulative
number of exoplanet discoveries versus time. It appears that the
number of known extrasolar planets is doubling every 27 months --
displaying a behaviour similar to Moore's law, but with a slightly
longer time constant. For illustation's sake, if you assume that the
Milky Way has 400 billion stars, and each star averages one planet per
star, then this relation(?) would predict that we will complete our
census of these worlds in late 2073 (hmm, I wouldn't bet on it). Data
taken from the Extrasolar Encyclopedia.
The distribution of known O-type stars, viewed from above the Galactic plane, with spiral arms (from Vallee 2002). O-stars are from the Maiz-Apellaniz et al. catalog, where I calculated distances using the Mv and (B-V)o values from Martins et al. 2005. Here I assume the Sun is 8 kpc from the Galactic center. The anticorrelation of the O-stars with the arms appears to be due to the magnitude-limited nature of the O-star catalogs. There tend to be more dark molecular clouds in the "gaps" where there are no O-stars.
B-V vs U-B color-color plot of OB and A0V stars. The plot gives an improved fit for deriving intrinsic (B-V) colors for OB stars using Johnson's Q-method (I had noticed that some of the formulae for deriving intrinsic B-V from the Q-method for high-mass members of the Sco-Cen OB association were giving more unphysically negative reddening values (E(B-V)) than one might suppose just from photometric errors. This plot shows why -- the previous calibrations do a somewhat poor job of fitting the "blue envelope" of colors for unreddened nearby B-type stars by attempting to force their
fit through (B-V, U-B = 0, 0) for A0V stars.
"The Lithium Plot": A crude age indicator for cool stars. This is a plot of stellar effective temperature (Teff) versus the equivalent width of the Li I 6707A line for stars in clusters of "known" age. Stars appear to be born with a more-or-less "cosmic abundance" of Li (roughly 1 Li atom for every 500 billion hydrogen atoms!). Li is burned in stellar interiors at relatively low temperatures (~1-2 megakelvin), but it is
burned relatively slowly in stars like the Sun since they have thin convective shells that do not allow the Li to reach great depths and high temperatures.
I'm also a weather and tropical cyclone nut... so here are some plots.
Atmospheric CO2 concentration
vs. annual global mean temperature. The statistical correlation
is very strong, however correlation does not necessarily imply
causation (but in this particular case, there is a well-studied physical
mechanism for understanding why more CO2 might lead to higher
temperatures!). There is, however, not a well-studied physical
mechanism for understanding why the number of pirates
and global mean temperatures should be correlated (save perhaps that pirates
are "cool"). Arrr!
Given the number of times I've heard non-experts say
on TV that higher atmospheric CO2 "will" translate into
worse hurricane seasons to come, I'm amazed that I've never
seen this plot anywhere. Arguably, ACE is the best metric of
hurricane season strength -- as the number of types of
storms of different strengths may be biased due to what
technology is available at the time to assess their
status. The plots above are very interesting. As the
previous plot showed a strong correlation (r ~ 0.9) between
CO2 and global temperatures, both the 1851-2007 and
1959-2007 CO2 vs. ACE plots show substantially weaker
correlations (r ~ 0.22) [perfect anticorrelation r = -1, no
correlation r = 0, perfect correlation r = +1]. But how
significant? Given the large sample size, r appears to
correspond to a significant correlation. For the satellite
era sample (1959-2007) r = 0.25, with the probability of
zero correlation being ~8%. For the whole sample
(1851-2007) r = 0.23, with the probability of zero
correlation being only ~0.4%. So while not overwhelming,
the current data are suggestive of a positive
correlation. Taken at face value, the measured slopes
are delta(ACE [kt^2])/delta(CO2 [ppm]) = 0.46+-0.19
(1851-2007) and 0.73+-0.46 (1959-2007). Given a mean ACE
value of ~86 kt^2, the 1851-2007 trend suggests that each
additional ppm of CO2 added to the atmosphere enhances the
potential accumulated cyclone energy for an Atlantic
Hurricane season by ~0.5 +- 0.2%. Over the past 10 years,
the CO2 in the atmosphere has increased on average by 2.0
ppm/yr, i.e. ~1% increase in potential ACE per year. Here
is a dangerous
extrapolation of these trends, which assumes that CO2
increases at the pace seen between 1959 and 2006, and the
Atlantic Hurricane ACE increases gently as measured in this
figure. Extrapolating the
quadratic trend in increasing CO2 between 1959-2006 would
suggest that by year 2100, the atmosphere will have ~673 ppm
of CO2 (assuming status quo increase) and a normal
Atlantic season would have ACE of ~250 -- equivalent to that
for the hyperactive 2005
hurricane season. Is this possible?
The crazy thing is that the Atlantic Hurricane seasons have
been unusually active since 1995 (ostensibly the Atlantic
Multidecadal Oscillation has returned us to a period of
enhanced cyclone activity). If you measure the same trends
during the 1851-1994 period -- the probability of no
correlation between CO2 and ACE for Atlantic Hurricane
seasons was 94% (r = 0.006)! During the 1851-1994 period,
the trend of CO2 vs. ACE was essentially flat: delta(ACE
[kt^2])/delta(CO2[ppm]) = 0.02 +- 0.17. Yet atmospheric CO2
increased by 26% from 285 ppm (1851) to 360 ppm (1994)
during that period! This suggests that the majority of the
positive CO2 vs. ACE trend has come just from adding the
hurricane seasons over the past decade or so. It will
be interesting to see in the coming decades whether the
mean ACE decreases again to levels seen during the quieter
1970-80's, or whether it continues to march upward...
Mean annual temperature for Pittsburgh from 1871-2006. I was curious to see if there was a demonstrable long term trend in temperature for my hometown over the past century (ostensibly due to global warming). The answer was surprising. If you fit a slope to all of the yearly data back to 1871, one finds a
negative slope (i.e. cooling), however the 90's and 00's
clearly buck this trend in the warming direction. Another interesting
find: the 90's were slightly warmer than the first 7 years of the
2000's (by ~0.3 deg F), however this is at the level of the
uncertainties in the decadal mean temperatures (~0.3-0.5 deg F). Most
interestingly, according to the NOAA data, the
warmest decades were (in order of highest temperature): 1890s, 1880s,
1930s, 1900s, 1920s, 1910s, 1990s, 1940s, 2000s (2000-2006). So while
the mean decadal temperatures in Pittsburgh during the 1990s and 2000s
are higher than during the 1960s, 1970s, and 1980s, they are clearly
not unprecendentedly high when compared to the late 19th and early
20th century.
Annual precipitation for Pittsburgh from 1837-2006. The slope of annual rainfall vs. time is slightly positive (wetter vs. time), but statistically consistent with zero. So, the NOAA data suggests that there has been no significant long-term trend in annual precipitation in Pittsburgh over the past century and a half. Also, the variance (i.e. year-to-year precipitation totals; a possible bell-weather of "extreme" changes) does not appear to be significantly different in the last three decades compared to before.
The Fed lowered interest rates to 2.0%. Since 1954, the rate has only been at or below this level 10% of the time. Fed Interest Rate 1954-2008 (monthly average)
Age distributions for 3 very different cities, all with populations around 30,000: Cambridge MA (college town), Bethel Park (suburb), and Sun City AZ (retirement city). Peak ages are 20, 42, and 77, respectively.
Basic Astronomical Data for the Sun (BADS?). If you work on stars other than the Sun (like me), and occasionally need to know the solar value, this may or may not be useful.