Intro to SQL
• Two components
• Data Definition Language (DDL):
• create table, etc.
• Data Manipulation Language (DML):
• select, insert, delete, update,
etc.
The basic “SELECT”
statement:
Select
From
Where
A1, A2,......AN
R1, R2,.......RN
condition
The basic “SELECT”
statement:
3
1
2
Select
From
Where
A1, A2,......AN
R1, R2,.......RN
condition
The basic “SELECT”
statement:
3
1
2
Select
From
Where
A1, A2,......AN what to return
R1, R2,.......RN relations
condition combine/filter
The basic “SELECT”
statement:
SELECT s.ra, s.dec, s.psfmag_g-s.extinction_g as g, s.psfmag_rs.extinction_r as r, s.psfmag_i-s.extinction_i as i, pm.pmra,
pm.pmdec, pm.pmraerr, pm.pmdecerr
FROM star as s
JOIN propermotions as pm ON s.objid = pm.objid
WHERE
s.ra BETWEEN 225.6 AND 225.8 and s.dec BETWEEN -2.0 and -1.8
AND CLEAN=1 AND s.psfmag_r <22
Load query into DR9 server
show SELECT count(*)
show check syntax and retrieval options
show clean photometry query
relevant URL’s from previous page:
http://skyserver.sdss3.org/dr9/en/tools/search/sql.asp
http://skyserver.sdss3.org/dr9/en/help/docs/
realquery.asp#cleanStars
Flags & Bitmasks
One thing that's important to fully exploit the SDSS
database is a good understanding of bitmasks.
A bitmask uses the bits in an integer as "toggles" to
indicate whether certain conditions are met.
http://www.sdss3.org/dr10/algorithms/bitmasks.php
Binary, decimal,
hexadecimal....
What??
https://www.youtube.com/watch?v=TFY8YuBLNKc
Go back to bitmasks page and show
search with flags again.
Science Interlude: Stellar Evolution and CMDs
CMD = Color-Magnitude Diagram
(Color vs. Mag)
HR = Herzberg-Russell Diagram
(Temp vs. Luminosity)
Magnitude
10Msun
M
ai
n
When stars form there are a small
number of high mass stars, and a
large number of low mass stars.
Se
qu
en Sun
ce
0.1Msun
Color/Temperature
Magnitudes, Luminosity and Fluxes
An astronomical source gives off a certain number of photons (per second per wavelength)
which we will call its luminosity, L.
The flux we measure from a source depends on its distance:
L
F =
4 d2
In the radio, fluxes are typically measured in Janskys, where:
1 Jansky = 10-26 watts / square meter / Hertz
Optical and infrared astronomers quantify the brightness of an object using the
magnitude system, which is the proportional to the logarithm of flux.
Magnitudes are define as:
m = 2.5 * log10(F) + 2.5*log10(F0)
where 2.5*log10(F0) depends on the photometric system.
he Magnitude System
Dotter et al. (2011)
Colors are defined as the ratio of fluxes, equivalently, the
difference between magnitudes, e.g., V - I
The star Sirius has an apparent magnitude mV = V = -1.4
The faintest stars observed with HST have apparent
magnitudes V ~ 30.
The Magnitude System
In addition to the UBVRI photometric system,
the SDSS system is also widely used (ugriz):
It is possible to transform between
photometric systems.
Apparent versus Absolute Magnitude
The observed flux of an object depends on its distance from us (F = L / 4*pi*d2).
Thus, when we observe an object, we are measuring its apparent magnitude (mv or V, mg or g)
The absolute magnitude of an object (MV, Mg, etc.) is related to its total luminosity.
Absolute magnitude is defined to be M = m when an object is placed at 10 parsecs (10 pc).
In PS#2, you will show that: M = m + 5 + 5*log10(d) where d is distance in units of parsecs
Science Interlude: Stellar Evolution
Stars form out of clouds of gas.
Out of a single gas cloud, many stars are born
at a single time:
-> lots of small mass stars
-> handful of massive stars
Stellar birth is clustered.
1kpc = 3 x 10^19 m ~ 3300 ly
Can we find traces of such events
in our Local Group?
Milky Way
halo
GC’s
bulge
disk
8 kpc
open clusters
halo
~200 kpc
05.03.2007
Sun
25 kpc
Sagittarius
Magellanic Clouds
Mürren - Saas-Fee-Course - E.K. Grebel
2MASS
infrared
31 image
Science Interlude:
several 1000 stars
Color Magnitude Diagrams
The Pleiades
~million stars
M80
Science Interlude: Color Magnitude Diagrams
M13
12 Billion years old
Chemical abundance similar to early universe
100 million years old
Chemical abundance similar to Sun.
Significant binary star fraction
Stellar Evolution
Out of a single gas cloud, many
stars are born at a single time:
-> lots of small mass stars
-> handful of massive stars
Mass
10Msun
M
ai
n
Se
qu
Highest mass star ~100Msun,
limit for fragmentation?
en Sun
ce
0.1Msun
Temperature
Lowest mass star 0.08Msun,
limit for nuclear burning.
Stellar Evolution
gravity pulls in
While a star is on the main sequence, it is in equilibrium.
Gravity balances pressure.
pressure
pushes out
Pressure comes from
heat generated by nuclear
fusion in star’s core.
More massive stars therefore must have a higher pressure/
temperature in their core, in order to maintain equilibrium.
The Sun’s Lifetime
The Sun formed 4 billion years ago,
and will live for another 4 billion years.
Sun is born
Now
Sun runs out
of hydrogen fuel
White dwarf
forms
The Sun’s Lifetime
At very end of evolution,
outer region expands and
disappears.
Inner region shrinks,
white dwarf left behind.
white dwarf
Stellar Evolution
Stars are ~black bodies, i.e., in thermal
equilibrium.The radiation has a specific
spectrum and intensity that depends only on
the temperature of the body.
Stellar Evolution
More massive stars must have a higher temperature to maintain equilibrium.
Stars are approximately black-bodies, thus
hotter stars are also bluer.
Along the main sequence, temperature, T,
and luminosity, L, are related:
L
L
T
M
4
3.5
Stellar Evolution - Lifetimes
How does stellar mass relate to a star’s lifetime?
The total energy released by a star in its lifetime is, Etotal:
Etotal = L * time
Nuclear fusion is turning mass into energy, which means Etotal = eff * M c2
Using the relationship between L and M on the main sequence:
t
M
2.5
Massive star lifetimes are much shorter than lower mass stars.
Magnitude/Mass
Stellar Evolution
10-100 million years
(very short lifetime)
10Msun
2-8 billion years
Sun
0.1Msun
Color/Temperature
10-100 billion years
(longer than age of Universe)
Magnitude/Mass
Stellar Evolution
How does Sun’s post-main
sequence evolution appear
in color-magnitude space?
10Msun
Sun
0.1Msun
Color/Temperature
Stellar Evolution
If stars of all masses form at same
time, can determine age
by noting which stars are just
evolving off of the main sequence.
Composite CMD for open
star clusters in the Milky Way
Science Interlude:
Color Magnitude Diagrams
HB =
Horizontal Branch
RGB = Red Giant Branch
MS =
main sequence
MS
WD = White Dwarfs
12 Billion years old
Chemical abundance similar to early universe
100 million years old
Chemical abundance similar to Sun.
Significant binary star fraction