Post on 19-Aug-2020
transcript
• Two components
• Data Definition Language (DDL):
• create table, etc.
• Data Manipulation Language (DML):
• select, insert, delete, update, etc.
Intro to SQL
The basic “SELECT” statement:
Select A1, A2,......AN From R1, R2,.......RN
Where condition
The basic “SELECT” statement:
Select A1, A2,......AN From R1, R2,.......RN
Where condition
3
21
The basic “SELECT” statement:
Select A1, A2,......AN From R1, R2,.......RN
Where condition
3
21
what to returnrelationscombine/filter
SELECT s.ra, s.dec, s.psfmag_g-s.extinction_g as g, s.psfmag_r-s.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
The basic “SELECT” statement:
Load query into DR9 servershow SELECT count(*)
show check syntax and retrieval optionsshow clean photometry query
http://skyserver.sdss3.org/dr9/en/help/docs/realquery.asp#cleanStars
http://skyserver.sdss3.org/dr9/en/tools/search/sql.asp
relevant URL’s from previous page:
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 showsearch with flags again.
Mag
nitu
de
Sun
10Msun
Color/Temperature
0.1Msun
CMD = Color-Magnitude Diagram (Color vs. Mag)
HR = Herzberg-Russell Diagram (Temp vs. Luminosity)
Science Interlude: Stellar Evolution
When stars form there are a small number of high mass stars, and a large number of low mass stars.
Main Sequence
and CMDs
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.
F =L
4�d2
The flux we measure from a source depends on its distance:
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.
The star Sirius has an apparent magnitude mV = V = -1.4
The faintest stars observed with HST have apparent magnitudes V ~ 30.
Color
Mag
nitude
The Magnitude System
Colors are defined as the ratio of fluxes, equivalently, the difference between magnitudes, e.g., V - I
Dotter et al. (2011)
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.
05.03.2007 Mürren - Saas-Fee-Course - E.K. Grebel 31
2MASSinfrared image
Magellanic Clouds
Sagittarius
bulge
disk
halo
Can we find traces of such events
in our Local Group?
Milky Way
Sun
8 kpc
~200 kpchalo
GC’s
25 kpc
1kpc = 3 x 10^19 m ~ 3300 ly
open clusters
Science Interlude: Color Magnitude Diagrams
The Pleiadesseveral 1000 stars
M80~million stars
100 million years oldChemical abundance similar to Sun.Significant binary star fraction
12 Billion years oldChemical abundance similar to early universe
Science Interlude: Color Magnitude Diagrams
M13
Mas
s
Sun
10Msun
Temperature
0.1Msun
Stellar Evolution
Lowest mass star 0.08Msun,
limit for nuclear burning.
Highest mass star ~100Msun,
limit for fragmentation?
Main Sequence
Out of a single gas cloud, many stars are born at a single time:
-> lots of small mass stars -> handful of massive stars
Stellar Evolution
gravity pulls in
pressure pushes out
While a star is on the main sequence, it is in equilibrium.
Gravity balances pressure.
Pressure comes from heat generated by nuclearfusion 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
Sun is born Now White dwarf formsSun runs out
of hydrogen fuel
The Sun formed 4 billion years ago, and will live for another 4 billion years.
The Sun’s Lifetime
At very end of evolution, outer region expands and disappears.
Inner region shrinks,white dwarf left behind.
white dwarf
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
L �M3.5
Stellar Evolution
More massive stars must have a higher temperature to maintain equilibrium.
Stars are approximately black-bodies, thushotter stars are also bluer.
L � T 4
Along the main sequence, temperature, T, and luminosity, L, are related:
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
t �M�2.5
Using the relationship between L and M on the main sequence:
Massive star lifetimes are much shorter than lower mass stars.
Stellar EvolutionM
agni
tude
/Mas
s
Sun
10Msun
Color/Temperature
0.1Msun
10-100 million years(very short lifetime)
2-8 billion years
10-100 billion years(longer than age of Universe)
Stellar EvolutionM
agni
tude
/Mas
s
Sun
10Msun
Color/Temperature
0.1Msun
How does Sun’s post-mainsequence evolution appearin color-magnitude space?
Stellar Evolution
Composite CMD for open star clusters in the Milky Way
If stars of all masses form at same time, can determine ageby noting which stars are justevolving off of the main sequence.
100 million years oldChemical abundance similar to Sun.Significant binary star fraction
12 Billion years oldChemical abundance similar to early universe
Science Interlude: Color Magnitude Diagrams
MS = main sequence MS
RGB = Red Giant Branch
HB = Horizontal Branch
WD = White Dwarfs