Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.
The (visible) (re-)birth of a star: IRAS 05436-0007 = V1647 Orionis
Search for the latest papers -- constantly updated:
Latest update: March 24, 2005
Much has happened since the last update. A brief summary of
some of the news follows.
- Grosso et al. (to appear in A&A sometime soon)
describe X-ray spectra of V1647 Ori taken on 2004 April 4.
They find variations in both the brightness and
hardness of the source over the 38,000 second exposure.
There is a very exciting hint of periodicity in the
X-ray brightness, which might provide information on
the physical nature of the X-ray luminosity.
The XMM telescope is scheduled to observe V1647 Ori
again very soon, for about 130,000 seconds starting
2005 Mar 24. The Chandra X-ray telescope is scheduled
to observe the source for 20,000 seconds soon thereafter,
around 2005 Apr 11.
- Muzerolle et al.
(ApJ 620, 107, 2005)
report on Spitzer near-IR photometry of V1647 Ori
in its early post-outburst phase (March 2004).
They find that the brightness of the star increased
by roughly the same factor of 15-20 across the
optical and near-IR, as their Figure 2 below shows
(pre-outburst are plus signs, post-outburst are
open and blue diamonds). Their vote on the FUor vs. EXor
question is "some of each."
- Kun et al.
(astro-ph 0408342)
use optical and near-IR data from 2004 Feb - 2004 Apr
to infer several properties of the system. Their
Figure 7 shows their model for the geometry of the system.
They conclude that the outburst was not due to a clearing
of dust from our line of sight, but rather due to an
increase in the luminosity and temperature of the source.
Based on their optical and near-IR data, they find no
evidence for magnetic accretion, and so vote for FUor
over EXor.
- The star has faded slightly in the optical and near-IR.
- Semkov
(IBVS 5578) provides VRI photometry from 2004 Aug 18
to 2004 Oct 03. There is a gentle rise in all passbands
to a peak around 2004 Sep, with perhaps a slightly
sharper decline afterwards.
- Gianluca Masi, R. Wilcox and F. Mallia report measurements
of V1647 Ori in unfiltered images taken with the
0.36 SoTIE reflector in Chile. They find
Date JD unfiltered mag
----------------------------------------
18 Mar 2004 2,453,083 16.15
14 Sep 2004 2,453,263 15.9
16 Mar 2005 2,453,446 16.6
----------------------------------------
Gianluca provides the following images showing the
evolution of the star over this time. The images
run from left (18 Mar 2004) to right (16 Mar 2005).
V1647 Ori lies at the apex of the fan-shaped nebulosity
at the top-center of the frame. The white bars indicate
two different long-term variables which Gianluca is studying.
Gianluca adds:
... we report also an evident fading of the nebula too,
which follows - of course - the brightness evolution of the star.
You can also look at an animated GIF
Gianluca made, showing these three images in a little movie.
- Ted Simon notes that preliminary reductions of near-IR
spectra taken with the IRTF indicates that
the overall brightness of V1647 Ori around 1-2 microns
has decreased by roughly a factor of 2 over the past
year. This is similar to the drop in the optical
shown in the image above...
Older update: September 1, 2004
In IAUC 8396, Aspin and Reipurth report that an image taken with the Gemini
guide camera on Aug 29 shows McNeil's Nebula and its central star to be
"in its elevated state." I interpret this to mean "still roughly as bright
as it was when it went behind the Sun," consistent with my
result from Aug 22.
older update: August 27, 2004
For your viewing pleasure, a graph showing the evolution of McNeil's Nebula in
the infrared, visible, and X-ray. This is a slightly updated version of one
of the figures from
Kastner et al. in Nature (July 22, 2004) .
You can find links to local copies of that paper below, in the July 23, 2004, entry.
older update: August 25, 2004
Two items today: a new paper, and a lousy (first?) attempt to measure the optical
brightness of the central star as it returns to the nighttime sky.
- Kun et al., in astro-ph 0408432,
analyze optical and near-IR measurements of V1647 Orionis from the winter
and spring of 2003-2004. They attempt to make a physical model of the
circumstellar matter in the neighborhood of the star. They also
suggest that the outburst was due to an intrinsic increase in the luminosity
of the central object (rather than a decrease in extinction),
and identify the object as an FUOr, rather than an EXor. That means
that it ought to stay bright for years ...
- ... which leads into the second item. I noticed that Orion is starting to appear
again in the eastern sky at sunrise, which means that we should soon be
able to observe V1647 again. Will it be fainter than it was in May (as one
would expect for an EXor), or the same brightness (as one might expect for
a FUOr)? I used the RIT Observatory's 12-inch telescope to take images
at a frighteningly large airmass on the morning of Aug 22, 2004, hoping
to find out. But it wasn't really successful ....
older update: August 18, 2004
Peregrine McGehee and coauthors describe the change
in optical and near-IR colors of V1647 Orionis from
its "quiescent" state to its outburst.
Vacca, Cushing and Simon present near-IR spectroscopy of
the object taken on March 9, 2004, with the SpeX instrument:
older update: July 23, 2004
Lots of new stuff in the past month.
- As mentioned in earlier notes, the Chandra X-ray Observatory
pointed to the new object several times during Spring 2004;
the X-ray flux increased by roughly a factor of 50 above
its pre-outburst value, which approximately matches the
increase in the near-IR flux.
-
V1647 Ori (IRAS 05436-0007) in Outburst: the First Three Months
a paper by Walter, Stringfellow, Sherry, and Pollatou,
provides a good deal of optical and near-IR photometry,
plus some spectroscopy.
-
National Public Radio's "Science Friday" talk show
included a segment on McNeil's Nebula on Friday, July 23, 2004.
older update: June 15, 2004
The star finally has an official name!
IAUC 8354 announces that the object is now called V1647 Orionis.
older update: June 12, 2004
Measurements of the new object in the mid-IR (low-res spectra
between 7.5 and 12.5 microns) and sub-mm (450 and 850 microns)
are reported in
astro-ph 0406089 , by Andrews, Rothberg and Simon.
A portion of their Abstract:
The 12 micron flux of this source has increased by a factor of 25 after the
outburst, whereas the submillimeter continuum remains at its pre-outburst
level. The bolometric luminosity has increased by at least an order of
magnitude, to ~34 L_sun, and is likely less than 90 L_sun. The mid-infrared
spectrum exhibits a strong and red continuum with no emission or absorption
features. The infrared slope of the spectral energy distribution characterizes
the illuminating source as a flat-spectrum protostar, in both its active and
quiescent states.
Peregrine McGehee presented
a poster paper on optical and near-IR photometry
of the environment of the new object, both before and during
outburst.
A longer paper based on the data is being prepared for
publication in ApJ.
Peregrine also points out that
a paper discussing FU Ori outbursts in a theoretical context,
astro-ph 0406264 by Lodato and Clarke,
may be of interest.
older update: May 13, 2004.
Doug Finkbeiner has created new color mosaics of the field around
McNeil's object, based on scans from the
Sloan Digital Sky Survey .
See them
down below .
Doug provides a warning:
Note that an asinh stretch is used
... and that the colors saturate to the correct
RGB color ratio instead of to white.
older update: Apr 16, 2004.
Bruce Gary's recent I-band photometry suggests that the
brightness of the object may have reached a first peak,
faded just a bit, then increased slightly before
starting to fade again. Could this very small secondary
peak be due to light echoes, rather than an intrinsic
increase in the light from the central source?
Bruce has some evidence that it very well may be due to
a light echo;
see
Bruce's speculations
on a light echo,
which are based on a careful analysis of the appearance
of the source's Point-Spread-Function (PSF).
older update: Apr 14, 2004.
A paper by Abraham et al. has appeared on astro-ph,
describing the infrared and sub-mm properties of the object:
They conclude that the object has a disk of about 0.5 solar masses,
a pre-outburst bolometric luminosity of 5.6 solar, and
is probably a class II protostar of age about 400,000 years.
older update: Apr 2, 2004.
The technical papers are starting to appear:
Older update: Mar 30, 2004.
You can hear Jay McNeil talk about his discovery on
an audio clip from NPR's "Weekend Edition".
In other news, we have learned that the Spitzer Space Infrared
Telescope not only took images of the field on March 15 with
the (mid-IR) MIPS instrument (we knew that already),
but also took images with its (near-IR) IRAC instrument
a week earlier, March 7.
Unfortunately, we haven't been able to look at this data yet ...
Older update: Mar 23, 2004.
Several items today: Joel Kastner tells me that Chandra has
successfully observed the object for a second time since outburst,
about 15 days after the first X-ray measurement. I've predicted
that the source will be more than twice as faint as it was
at the earlier epoch; Joel tells me he'll be able to make
a good measurement sometime within the next week or so.
I've also come across a nice, big, false-color mosaic
of the M78 region which includes the new object.
Go to the
2MASS Atlas Image Gallery of HII regions, star formation regions,
and reflection nebulae
and scroll down about halfway through the page. It was hard
for me to see on the little thumbnail, but the full-size
version shows the object very clearly.
Note that this is based on images taken several years ago,
so it's a "pre-outburst" IR image.
Old update: Mar 22, 2004.
The Gemini Observatory has put out
a press release
which includes some nice pictures of the star,
some astronomers (including Jay McNeil),
and an artist's rendition of what may be happening.
Old update: Mar 16, 2004.
Bruce Gary, of Hereford, Arizona, has been following the
optical evolution of the new star since mid-February.
He finds that in the R and I bands,
the star has reached its peak brightness
and is now starting to fade.
For all the details, look at
Bruce Gary's measurements of the new star.
Old update: Mar 15, 2004.
César Briceño has made a movie showing the evolution of the
new star and its nebulosity in the visible part of the spectrum,
based on images taken with
the 1m Schmidt telescope of Llano del Hato National Astronomical Observatory
in Venezuela. Go to
Cesar's movie page to see the animation.
Also, the Spitzer satellite acquired infrared images
of the star last night.
Old update: Mar 8, 2004.
Joel Kastner reports that a Chandra X-ray image shows
the new star to be much brighter than it was in
the pre-outburst X-ray image.
Rah! More analysis soon from Joel ....
Old update: Mar 1, 2004.
Arne Henden provides
a color composite in BVI
of the new object, taken Feb 22, 2004.
Old update: Feb 28, 2004.
See some color pictures
of the field from 199 and 2002.
Old update: Feb 21, 2004.
Peregrine McGehee reports that the literature
contains several images of the field
taken in years past.
You can see some scanned versions of these images
and speculation on what they mean
in the
Feb 21
section of this page, below.
There's also a very pretty color picture of the area
made by David Schlegel
from SDSS scans of the area.
Old update: Feb 20, 2004.
Joel Kastner describes X-ray emission from the new object
in a Chandra image
taken in 2002.
It appears that Chandra will be looking at the new
star as a Target Of Opportunity in early March!
The position of the new star, based on 2MASS K-band image from 1999,
is
RA = 05:46:13.1 Dec = -00:06:05 (J2000)
In the past few weeks, a new star
has appeared to our visible instruments
in the Milky Way Galaxy.
It's not a "nova" or "supernova" --
the result of a gigantic explosion near
the end of a star's life --
but a stellar birth!
In one particular region of the Milky Way
lies a giant cloud of gas and dust,
which astronomers call M78.
Image courtesy of Daniel Verschatse
(Antilhue Obs.)
Young stars are forming out of this cloud,
and their light excites the remaining gas,
causing it to glow.
We call the beautiful glowing cloud a nebula.
Note that the region to the lower-right of M78
is rather dark:
In this region, the thick dusty clouds block light from
stars hidden behind them.
Only a few stars manage to penetrate the gloom.
Because blue light is scattered and absorbed more
easily than red light,
these stars appear redder than they truly are.
Let's concentrate on a small region near the center
of the box.
Way back in 1951,
astronomers photographed this region
in red light as part of the Palomar Observatory
Sky Survey (POSS).
The image shows a few stars, with a nice pair
near the center.
In 1990, a second photographic survey (POSS II)
again photographed the region in red light,
and found, well, pretty much the same picture.
The pair of stars near the center is again the most prominent
feature.
In 1998, the
2MASS
project surveyed the area, this time at infrared
wavelengths.
Because infrared light has a longer wavelength than
visible light, it
ought to penetrate the dusty clouds more deeply
and show us any objects hidden within.
You can see several new stars, to the lower right
of the bright pair, which aren't apparent
in the visible-light images.
Hmmmm.... These stars must be hidden within
cocoons of dust and gas.
In January, 2004, however,
ordinary visible-light photographs of the region suddenly revealed
a new object.
The first report came from J. W. McNeil, of Paducah, Kentucky,
who noticed the new object on Jan 23, 2004.
Compare these two pictures taken by Japanese
astronomer Yasuo Sano: in 2001, on the left, and in 2004, on the right:
The right-hand picture above was taken on February 11, 2004.
The picture below, also from Sano-san, was taken
one night later.
Sano-san's pictures indicate that the star is growing brighter
quickly, within the span of a single day.
His measurements:
object YYYYMMDD(UT) mag code
IRAS05436-0007 20040211.455 14.46CR San.VSOLJ
IRAS05436-0007 20040212.421 14.07CR San.VSOLJ
Yasuo Sano (Nayoro, Hokkaido,Japan)
Instruments: 28cm-SCT + ST-9E exp 30sec(2004/02/11).
25cm-NT + ST-9E exp 30sec(2004/02/12)
Comparison stars: Henden 3 star R mag
Kamil Hornoch also finds that the object becomes brighter:
Date: Fri, 13 Feb 2004 11:29:47 +0100
From: Kamil Hornoch
Subject: New nebula near M78: additional photometry
...
Most southern star (and brightest star included in a new nebula)
increased its brightness of about 0.20 mag between Feb. 11.913 UT
and 12.908 UT.
Let's compare the location of this new object in the visible
to the infrared picture taken several years ago.
Here's a zoomed-in view of the optical picture --
click on it to reach a "blinking" page,
where you can switch back and forth between
visible and IR.
Yes! The star really was there back in 1999 (and probably for
thousands of years earlier), but it has just now become
visible in the optical.
Why?
It must be blowing away the cocoon of dust and gas which
surrounds it -- we think all young stars have
strong winds of this kind.
Over the past few years,
the wind has managed to clear enough dust
that the visible light emitted by this young star can finally
make it all the way to Earth.
The position of the new star, based on 2MASS K-band image from 1999,
is
RA = 05:46:13.1 Dec = -00:06:05 (J2000)
Arne Henden provides a nice R-band image of the new star
taken with the 1.0-m telescope at US Naval Observatory
in Flagstaff, Arizona. He also provides photometric
calibration for some of the nearby stars -- see the
table below.
This is just a small sample of Arne's measurements for a subset of
stars marked in the chart. See the full table with all the data below.
ID RA Dec V B-V U-B V-R R-I
--------------------------------------------------------------
A 86.581120 -0.088877 14.853 1.577 99.999 1.081 1.081 LkHA 301
B 86.578727 -0.093920 16.290 1.847 99.999 1.279 1.345 variable?
C 86.485580 -0.182250 14.971 1.137 99.999 0.713 0.609
Gianluca Masi points out that star "B" is apparently variable in
brightness. Taichi Kato and Brian Skiff mention that this star
exhibits emission lines, and may very well be a T Tauri variable.
The companion, star "A", also known as LkHA 301, is a known T Tauri
star, and a variable. It is not surprising to find very young
(and variable) stars in this star-forming region.
Added Feb 13, 2004, EST.
Gianluca Masi notes that this object was apparent
in the optical several decades ago. He writes:
the object was observed two days ago by me and Franco Mallia, using the
Tenagra II telescope. The star was really evident (the images were grabbed
around 11.2 feb UT) and its astrometry reported to CBAT. Here is the image:
http://www.campocatinobservatory.org/IRAS_05436_0007.jpg
I have also found an image of 1960s where the same feature is visible. This
seems to suggest a repeated outburst of the source.
I've sent a report to CBAT. I saw evidence of the "nebula" starting on Nov
2003, since then showing an incresing brightness.
I suggest to closely monitor the object for the remaining season.
Gianluca points to this image of M78 (left below), part of the
SEDS Messier gallery, available at
http://www.seds.org/messier/large/m78.gif
The photograph is part of the book The Messier Album,
by John H. Mallas and Evered Kreimer, published in 1978
by Cambridge University Press. The image was taken
by Kreimer from his home in Prescott, AZ, (alt 5400 feet),
on Oct 22, 1966 with a 12.5-inch f/7 Cave reflector,
a 15-minute exposure only Tri-X cooled to
-109 F in a dry-ice camera. The film was processed in
D-19 for 4 minutes, and (alas) a dodging mask was used
in making the print. Tri-X peaks in the blue part of the
spectrum.
The image on the left is the "old" one, from 1966;
the image on the right is a half-size version of Sano-san's
picture of Feb 12, 2004.
Note that the nebulosity in 1966 is brightest
at the top (north) end, whereas the 2004 event
is brightest at the bottom.
Added Feb 15, 2004
Brian Skiff warns that it won't be easy to make accurate
meassurements of the new star's brightness:
Because of the very strong reddening of this star, it will
almost certainly be necessary for folks to use standard photometric
filters, since color terms among various chips and varying temperatures etc
on the same chip will be impossible to compensate for.
In addition, without the additional information of the the
photometric aperture used, as well as details on how the strong and
strongly-varying background has been dealt with, comparisons among
different observers will be unworkable.
Large image scales (long focal-length and small pixels) will be
required to deal with this star. The gradient of the nebula near the
star might be modelled by a tilted plane (or quadratic) to determine
the sky level at the star itself. Annular 'sky' zones probably won't
work. The 'star' apertures will have to be very small (few arcsec only).
Added Feb 17, 2004
At last the big guys have become involved.
Aspin and Reipurth report that near-IR images
taken with the Gemini 8-m telescope show
that the object has brightened by about 3 magnitudes
in JHK, relative to the 1998 2MASS measurements.
Gemini spectra reveal strong features of CO
and hydrogen Brackett-gamma in emission in the
IR; in the optical, H-alpha shows emission with
a P Cygni profile.
Suggested readings for reports of similar events:
-
Eruptive phenomena in early stellar evolution ,
Herbig, ApJ 217, 693 (1977)
-
The 1993-1994 Activity of EX Lupi ,
Herbig, PASP 113, 1547 (2001).
The abstract to this paper reads:
EX Lupi is a classical T Tauri star (and the EXor prototype)
subject to
sporadic outbursts. The historic record shows that
it remains at about V=13.2
(or mpg=14.7:) for extended periods, from which it
has been observed to
brighten to as much as V=8.4 (on one occasion
in 1955-1956). During 1993-1994
the star remained slightly above normal minimum,
at about V=12.8, and from that
level rose to three maxima at V=11.4 and on
other occasions to about V=12.0. At
minimum light an M0 V absorption spectrum is present.
At outburst this spectrum
is veiled by a hot continuum (well shown by an IUE exposure),
the equivalent
widths of the optical-region emission lines decrease,
and reverse P Cygni
absorption components appear at the higher Balmer
lines. The outbursts are
believed to be due to episodic infall onto the M0 star.
Added Feb 19, 2004
The
Sloan Digital Sky Survey
detected a very faint source at the position of the new star
several times in the past few years.
Here's an image taken in early February, 2002, in the z-band;
(the SDSS z-band has an effective wavelength of about 8950 Angstroms
and a width of about 1140 Angstroms).
A closeup shows the object clearly, plus some very faint
emission from nebulosity to its north.
Added Feb 20, 2004
Selected tidbits from IAU Circular 8290:
- M. Halderman did _not_ detect the star and or nebulosity
on Feb 6, 2003
- M. Halderman _did_ detect the star and very faint nebulosity
on Nov 26, 2003
- R. Croman detected the star and nebulosity
on Dec 30, 2003
Which brings us chronologically
to the first person who apparently noticed something
out of the ordinary:
amateur astronomer Jay McNeil, who first noticed the recent outburst
in an image taken on January 23, 2004.
You can read
Jay McNeil's own account of the events
(and my local copy ).
in the February, 2004, issue of the Houston Astronomical Society's
newsletter.
Astronomy Picture of the Day
has chosen this new object as its topic for
their entry for Feb 19, 2004.
APOD also provides a nice color picture taken by
Adam Block
as part of the
Kitt Peak National Observatory Visitor Program.
A larger version can be found in the APOD entry for Feb 19, 2004.
Here's a closeup of an X-ray image near the new star,
courtesy of Joel Kastner and
the Chandra data archive.
The field is about 4x4 arcminutes, with North up and East to the
left. The new object is the very weak source at center;
stars A and B are the bright pair to its north-east,
as in optical and IR images.
Added Feb 21, 2004
Peregrine McGehee points out a couple of existing
papers which discuss the new object and its neighbors:
-
Parsec-Scale Jets From Young Stars
by Eisloffel and Mundt,
Astronomical Journal v.114, p. 280-287 (1997).
It contains images in [SII] which show nebulosity
to the north of the new object.
-
Dust Continuum Imaging of the HH 24 Region in L1630
by Lis, Menten and Zylka,
The Astrophysical Journal, Volume 527, Issue 2, pp. 856-865 (1999).
The authors mapped the region in the continuum at
350 and 1350 microns.
They discuss the case of a source coincident with the new
star (which they call LMZ 12) in some detail.
A color picture from the SDSS appears at the end of today's section.
Here's a chart from the paper by
Eisloffel and Mundt
showing [SII] emission from the area.
North is up, East to the left.
The two stars just to the left of the label
"HH22" are the ones I've called "A" and "B" in charts above.
Watch out for some image distortion on the left -- I couldn't get
the page to sit flat on the scanner's platen :-(
A closeup around the new object's area:
[SII] on the left, from October, 1995,
and R-band on the right, from mid-Feb, 2004:
Zoom in even closer:
again, [SII] from 1995 on the left,
R-band from Feb 2004 on the right:
A deeper image from the paper shows the region around
the new star more clearly;
click on the image below for a larger version.
As
Eisloffel and Mundt
state, what we see to the right (west) of the double
star is a combination of two different sources:
- the bright knot of nebulosity due west of the
double stars, marked "A" in the chart above,
lies at the end of a jet, marked by
a series of condensations. This
jet presumably originates in a star somewhere
to the east (left) of the chain, but
Eisloffel and Mundt couldn't find any source
in the right place
- the nebulosity labelled "HH23", to the north
of the double stars, appears to be the
terminus of a jet coming from the south.
It looks like the source might be
near the cross, which marks the infrared
source IRAS 05436-0007.
That is also the location of the new star which
has just recently become visible in the optical.
These images suggest (to me, at least) that
the blob of nebulosity "A" just north of the
new star may not be coupled to it directly;
it may very well be in the foreground or background.
However,
on the other hand, when we go back to look at Kreimer's
image back in 1966 (shown below at far right)
we see that BOTH the southern core (corresponding
to the IRAS source and newly visible star)
AND the northern blob "A" both appear bright!
So this is a mystery: if
the knot "A" belongs to the west-going jet from HH22,
and the new star makes a north-going jet upwards
towards HH23,
why should both knot "A" and the new star appear
brighter than usual at the same time back in 1966?
Is it possible that the knot "A" is a product of
both outflows, which happen to run into each other
by some coincidence?
On to the paper on infrared imaging by
Lis et al..
Their figure 5 shows the area around HH22,
taken in January 1997:
Let's compare it to the [SII] image of Eisloffel and Mundt:
It seems that
- the new star, which Lis et al. called "LMZ 12",
is a strong source of far-IR continuum radiation.
- the far-IR emission to its north may be
due to the outflow from LMZ 12, or from HH22,
or from both
Lis et al. provide measurements of LMZ 12 at several passbands
in the far-IR in their Figure 6:
the two longest, 350 and 1300 microns, they determined themselves
in January, 1997;
the four other data are taken from IRAS, which observed
the area sometime in the early 1980s.
Lis et al. describe how they were unsatisfied with the
IRAS catalog entry at 60 microns and re-derived the flux at that
wavelength.
Given what we know now about the variability of the object,
it's not clear that combining measurements taken 15 years apart
is a good idea.
This color composite comes from the Sloan Digital Sky Survey:
blue = the 'g' filter (centered on 4700 Angstroms),
green = the 'r' filter (6200 Angstroms, includes H-alpha),
red = the 'i' filter (7500 Angstroms).
Thanks to David Schlegel and Jill Knapp for
providing it!
Click on the image for the full-size version.
Added Feb 28, 2004
Thanks to Steve Kent and
the Sloan Digital Sky Survey ,
here are two pictures of the field from a few years back:
one from 1998 and another from 2002.
Taken in November, 1998:
Taken in February, 2002:
Added Mar 1, 2004
Arne Henden has made a nice color composite from
images in B, V and I, taken with the USNO 1.55 m telescope
on Feb 22, 2004.
Click on the image below for a full-size version.
Added May 13, 2004
Doug Finkbeiner provides _big_ color mosaics from the Sloan
Digital Sky Survey. Click on each thumbnail to download
the full image. Beware -- they are around 8 MB each!
First, a composite of the g, r, i passbands:
Next, a composite of the r, i, z passbands (which go into the
near-infrared):
For more information
Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.
