A Standard Cell Library for Student Projects

1

Short-Term Variability in Quasar Magnitude
Brian T. Fleming1, Julia Kennefick2, S. Bursick2
1Illinois Institute of Technology, Chicago, IL USA
2University of Arkansas, Fayetteville, AR USA
Understanding Quazi-Stellar Objects (QSOs)
Quasars Selected for Variability Study
Purpose of Study

• First observed in 50s as radio sources without a
  corresponding visible source.
• 1960 - 3C 48 tied to faint blue star-like object
  Spectrum contained anomalous emission lines.
  Classified as unknown
• 1963 3C 273 determined to have a redshift of
  z0.1592
• Traveling away from Earth at 44,000 km/sec
• Nearly 2 billion light years away (Using Hubbles
  Law )
• Dubbed Quazi-Stellar Objects because they looked
  like stars
• Today it is known that quasars are galaxies with
  super-massive black holes differentiated from
  the term QSO
• Only about 10 are radio sources (Radio Loud
  Quasars)
• Excited matter accelerated in the accretion disk
  of the black hole give off staggering amounts of
  energy (1.8 x 1046 ergs/s for 3C 273 4.7
  trillion suns)
• Most distant and luminous objects known

• Five known Quasars were selected using the NASA
  Extragalactic Database (NED) for this study
• Three areas of sky were observed using the NFO
  Webscope with two of those areas containing two
  separate quasars resolvable by the telescope
• In order to help find the quasar in each image,
  the quasars relationship to neighboring objects
  was established. In figures 3-5 below the quasar
  is marked by the purple circle.

• Observe five (5) quasars for 45 days
• Can the QUEST quasar variation be detected
• Look for variation in the other quasars
• Challenges
• Short time interval
• Faint magnitudes push limits of the NFO webscope
• Will help set standard for quasar variability
  astronomy limits

Fig. 7 A Quasar. The outer edge of the
accretion disk is barely visible partially
eclipsing the luminous region6
Procedure
Take Images as often as possible over study time
period (45 days)
Sequential Logic
Fig. 3 HS 16033820
High magnitude and redshift Magnitude
15.9 Redshift 2.51
Monitor change in nearby stable stars to remove
interference
Quasar Detection and Identification
Fig. 4 VCV J162021.8173623 Magnitude
16.4 Redshift z 0.55510 VCV J162011.3172428 Ma
gnitude 15.5 Redshift z 0.11244

• Quasars usually appear as stars in optical
  wavelengths
• Too distant to resolve as galaxies with most
  telescopes
• Differentiated from stars using spectroscopy
  most common method of detection

The NFO Webscope
Subtract average stellar variation from quasar
variation
Record day to day quasar magnitude variation

• Robotic Telescope
• 24 Inch diameter
• Capable of resolving objects with m18 with
  stacked images

Quasar Variability Observed
Fig. 5 Previously studied for variability. QUEST
J150724.0-020212.1 Magnitude 14.5 Redshift
1.090 QUEST J150706.7-020728.9 Magnitude
17.3 Redshift 1.920
Fig 8 Red Filter VCV J162011.3172428 No
appreciable variation. Slight downward trend
within error range. 13 days observed.

• Stars fall in highly populated color region
  (fig.1 left4) due to stellar cores being
  primarily dominant fusion cycles
• Quasars (and other anomalous objects) will
  usually outside the populous region

Fig 9 Red Filter VCV J162021.8173623 No
appreciable variation. Slight upward trend within
error range. 13 days observed.
Quasar Variability

• Type of matter in the accretion disk is not
  constant with time
• Galaxies, while primarily Hydrogen, are not
  uniform
• Supernova remnants will be rich in heavy elements
• Amount of matter is also not constant
• Larger and older galaxies tend to have pockets of
  heavier concentration of matter due to gravity
• Spiral galaxies have spaces between the arms
• Over time, these fluctuations will cause
  noticeable variation in the wavelength (and
  magnitude) of light emitted

• Spectra of the Anomalous Objects that reveal
  strong emission lines for Hydrogen (primary
  element in a galaxy) identify objects as quasars
  (fig.2 right5)

Fig 10 Red Filter HS 16033820 No appreciable
variation. 9 days observed
The QUEST Quasar Variability Survey 6

• QUEST survey concluded that with a 80 confidence
  level, about 75 of quasars that they surveyed
  will show variability over a 26 month period6
• 50 will show at least 0.15 mag variation over 2
  years
• Nearly all will vary by at least 0.05 mag over 15
  years
• The QUEST survey was the first survey to use
  variation as a means of quasar discovery as
  opposed to the standard multi-color analysis
  method

Fig. 6 A plot of magnitude versus time for the
QUEST J140621.6-012121.2 quasar.6
Primary References
3Quasar Astronomy Daniel W. Weedman, Cambridge
University Press, 1986 4University of Tokyo,
Multicolor Survey for High Redshift Quasars,
S. Oyabu, 1998 5The Astrophysical Journal, 2DF
QSO Redshift Survey, S.M Croom, 1998 6The
Astrophysical Journal, New Quasars Detected Via
Variability in the QUEST1 Survey, A.W
Rengstorf, May 2004