astronomers and data

Mining the UNKNOWN in the Sloan Digital Sky Survey

Patrick HallAssistant Professor

Dept. of Physics & AstronomyYork [email protected]

Astronomers and Data

•Problem: research astronomers have so much data they can’t do all the cool science possible with the data.



•Solution: more research astronomers!




•Encourage your MP and MPP to support higher education, and astronomy research.




•Encourage your MP and MPP to support higher education, and astronomy research.

•Meanwhile, become a research astronomer yourself...

…using the Internet

•Find sungrazing comets in SOHO images (click on FAQs for details): http://ares.nrl.navy.mil/sungrazer

•Find interstellar dust particles in aerogel collectors returned to Earth from the Stardust mission: http://stardustathome.ssl.berkeley.edu

•Galaxy Zoo: http://GalaxyZoo.org

http://ares.nrl.navy.mil/sungrazer

http://ares.nrl.navy.mil/sungrazer

http://stardustathome.ssl.berkeley.edu/

http://galaxyzoo.org/

http://galaxyzoo.org/

...using the SDSS (the Sloan Digital Sky Survey)

• 120-Mpix camera imaging 1/4 of the sky in 5 colors.

• About 1 in every 2000 detected objects is selected for further study via spectroscopy, either because the object is a bright galaxy or because it has odd colors.

• 640 spectra obtained simultaneously via optical fibers.

• Left: SDSS telescope (with its dome rolled off out of sight)

• Below: optical fibers (orange) being plugged into a spectroscopic plate (large metal disk with holes)

...using the SDSS (the Sloan Digital Sky Survey)

• 120-Mpix camera imaging 1/4 of the sky in 5 colors.

• About 1 in every 2000 detected objects is selected for further study via spectroscopy, either because the object is a bright galaxy or because it has odd colors.

• 640 spectra obtained simultaneously via optical fibers.

• Automated software classifies each spectrum as a star, galaxy, quasar, etc.

• Spectra that can’t be classified are labelled “unknown”.

Online SDSS Research•GalaxyZoo.org - inspect galaxy images

from the Sloan Digital Sky Survey (SDSS)

‣previous result: statistically equal numbers of spiral galaxies are wound counter- and clock-wise

‣current goals: verify candidate merging galaxies, identify overlapping galaxies and ring galaxies, ...

‣serendipitous result: Hanny’s Voorwerp

• Hanny’s Voorwerp is the false-color blue-purple object in the SDSS cutout image above. Its spectrum shows it is gas so hot and highly ionized that it must have been illuminated by a quasar, either now or in the past.

Online Astronomy Research

•GalaxyZoo.org - inspect galaxy images from the Sloan Digital Sky Survey (SDSS)

‣previous result: equal numbers of spiral galaxies are wound counter- and clock-wise

‣current goals: verify candidate merging galaxies, identify overlapping galaxies and ring galaxies, ...

‣serendipitous result: Hanny’s Voorwerp, a possible “light echo” of an ancient quasar outburst

• SDSSUNKNOWN - RASC members & invited guests can help identify “unknown” spectra from the SDSS

The SDSSUNKNOWN project•Of the 1.2 million+ SDSS spectra, about

1.6% (20,000) are classified as UKNOWN by automated software.

The SDSSUNKNOWN project• Of the 1.2 million+ SDSS spectra, about 1.6%

(20,000) are classified as UKNOWN by automated software. Visual inspection following simple rules can classify most of those spectra. That is the goal of this project.

The SDSSUNKNOWN project• Of the 1.2 million+ SDSS spectra, about 1.6%

(20,000) are classified as UKNOWN by automated software. Visual inspection following simple rules can classify most of those spectra. That is the goal of this project.

• These UNKNOWN objects include:

• normal objects missed via software bugs/limitations

• supernovae

• moving objects (comets & asteroids)

• uninteresting glitches in the data

• interesting and unexpected surprises...

•Previously unrecognized, old, cool white dwarf only 100 light years from the Sun (discovery paper published this month in The Astronomical Journal)

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• Rapid optical transient of unknown origin. Images are spaced 72 seconds apart in the order they were taken: orange (no OT), red (faint OT), ultraviolet (bright OT), infrared, and green. The OT increases in brightness by 4 magnitudes (a factor of 40) in 72 seconds. Up to 15 orphan gamma-ray bursts are expected in SDSS....

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SDSSUNKNOWN: Science via Google Group

•To join the SDSSUNKNOWN effort, visit the website http://groups.google.ca/group/sdssunknown

http://groups.google.ca/group/sdssunknown



•You’ll need to create a Google groups account (using any e-mail address you want) if you don’t have one.




•You’ll need to create a Google groups account (using any e-mail address you want) if you don’t have one.

•Then you can request group membership. You’ll be added within a few days, and can start classifying.



• To join the SDSSUNKNOWN effort, visit the website http://groups.google.ca/group/sdssunknown

• You’ll need to create a Google groups account (using any e-mail address you want) if you don’t have one.

• Then you can request group membership. You’ll be added within a few days, and can start classifying.

• Group members can edit the group pages containing classifications of previously unknown objects and post discussion messages with general or specific questions.


Information for Classification: SkyServer Object Explorer

•For each unknown object, links are provided to SDSS images and spectra via the SkyServer Object Explorer.


•For each unknown object, links are provided to SDSS images and spectra via the SkyServer Object Explorer.

•By applying a set of rules based on the appearance of the image and the spectrum, each object can be classified (though some will remain as “unknown”).


• For each unknown object, links are provided to SDSS images and spectra via the SkyServer Object Explorer.

• By applying a set of rules based on the appearance of the image and the spectrum, each object can be classified (though some will remain as “unknown”).

• Sample rule: if it looks like a galaxy on the images, it is a galaxy... unless it’s a comet, asteroid, superposition, bright star, spurious object near a bright star, etc.


• For each unknown object, links are provided to SDSS images and spectra via the SkyServer Object Explorer.

• By applying a set of rules based on the appearance of the image and the spectrum, each object can be classified (though some will remain as “unknown”).

• Group members can enter their classifications of previously unknown objects, as well as post discussion messages with general or specific questions.

• Together, we’ll classify all objects that can be classified.


• To join the SDSSUNKNOWN effort, visit the website http://groups.google.ca/group/sdssunknown

• You’ll need to create a Google groups account (using any e-mail address you want) if you don’t have one.

• Then you can request group membership. You’ll be added within a few days.

• Membership open to RASC members and their guests, but the group is not publicly visible.


Classifying Spectra: Sample Rules

• If it looks like a galaxy on the images, it’s a galaxy... but beware of comets, asteroids, superpositions, bright stars, spurious objects near bright stars, etc.

• If it has a featureless blue spectrum, and an X-ray or radio cross-identification, it’s a blazar (a quasar seen face-on, so that emission from a relativistic jet swamps all other emission).

• If it is pointlike on the SDSS image and has a proper motion of >1 arcsecond per century, it’s a star.

• If it looks like a little rainbow on the SDSS image, it’s an asteroid.

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