NED Frequently Asked Questions -- NED and other catalogs
Catalogs and NED
(Latest revision: 29 May 2009)
Q:Why doesn't NED have any information about the Sun, the planets, or the stars?
A:NED is an extragalactic database.
Data and references for Galactic objects may be retrieved from
maintained by the Centre de Donnees astronomiques de Strasbourg, France.
Similarly, solar system and planetary data may be retrieved from
NASA's Planetary Data
System at JPL.
Q:What images are included in NED?
Most of the images NED holds on line
are optical, infrared, and radio images of galaxies, though we do
have some UV and X-ray images as well. We also collect
HI spectra, isophote maps, and other graphical
representation of extragalactic data.
NED can also display an image of a given object from the
Digitized Sky Survey
using one of the Object Search options, or the Image Search option, all
available on NED's Home Page.
Q:How may I contribute my FITS images or spectra to NED?
A:Please leave a
comment with your name and email address so that we may contact
you. Or you may send email to the
Q:What is the difference between Strict and Liberal in the IAU-format search?
A:The IAU names are in the form:
H = hours of RA
D = degrees of DEC
M = minutes of RA or DEC
S = seconds of RA or DEC
+ = + or - declination
d = decimal numbers.
2214+3307 would represent: 22h14m +33deg 07'
2214+337 would represent: 22h14m +33.7 deg
The Strict convention understands the input as a truncated
version of the coordinates and adds a half decimal to the last digit
given in RA and Dec, then searches for all objects within a radius
equal to the larger of the half decimal suffixes.
→ 22h 14m +33deg 7'
Since the range in position is up to
22h 15m +33deg 8'
the center position is determined
by adding half a decimal to the input position
22h 14.5m +33deg 7.5'
22h 14m 30s +33deg 7' 30"
This position becomes the center of the search circle.
Since the center is within 30 sec and 30 arcsec from the
input position, the radius of the search should cover the
largest distance, in this case 30 seconds of time.
The Liberal convention assumes that the last digit could be either truncated or
rounded, and considers the resulting possibilities. NED then searches
for all objects within the largest circle containing all the possibilities.
Input: 22142+332 could be:
221420+3320 → 221429+3329
22h14m20s +33deg 20' → 22h14m29s +33deg 29'
221412+3312 → 221418+3318
22h14m12s +33deg 12' → 22h14m18s +33deg 18'
So, the search is between the extremes of these positions:
Q:Not all of the IRAS catalog entries seem to be in NED. Are some sources missing?
A:Yes. When we loaded the IRAS catalogs,
we used various filters to improve the chances of a source being extragalactic.
22h14m12s +33deg 12' → 22h14m29s +33deg 29'
which would make the center at:
22h14m20.5s +33deg 20' 30"
The search radius which encompasses all possible interpretations
of the IAU name is then:
10.7' = 10' 42"
FSC sources in NED were chosen using the following "color" and quality
1) F(25)/F(60) < 2.0 AND
2) Q(60) ≥ 3
PSC sources used the same flux and color filters, and added three
additional filters based on the IRAS "cirrus" flags:
Q:There are only 1500 entries in the Markarian
catalog. Yet NED has some Markarian numbers over 1500. Where do these
extra numbers come from?
A:In 1986, V. A. Lipovetsky and J. A. Stepanian
collected all the Markarian objects from the fifteen published lists into a
complete "First Byurakan Survey." This list, never published but privately
circulated, included an additional 32 objects given provisional numbers from
9001 to 9032. A few of these provisional numbers have appeared in the
literature, so we have put all of them into NED.
1) cirr1 < 9 AND
In addition, all PSC sources in the areas of the LMC, SMC,
M31, and M33 were loaded into NED and flagged as being within
the boundaries of those galaxies.
2) cirr2 < 7 AND
3) cirr3 < 75
Then, in 1989, Markarian, Lipovetsky, Stepanian, L. K. Erastova,
and A. I. Shapovalova published their complete Markarian catalog in
Communications of the Special Astrophysical Observatory, No. 62
as "The First Byurakan Survey. A Catalogue of Galaxies with UV-continuum." This
catalog has an additonal 15 objects numbered from 1501 to 1515, 14
from the 32 new objects in the 1986 list, and one new. We have also put these
15 numbers into NED, so the 14 new objects in common to the 1986 and 1989
lists carry two Markarian numbers.
Q:There is a gap in the Fairall numbers between 1185 and 1201. Do these objects exist?
A:No. Fairall's original lists (see Fairall,
MNRAS 233, 691, 1988 and references therein) contained
data for 1185 compact and
bright-nucleus galaxies, while the latest paper (Fairall and Woudt,
MNRAS 366, 267, 2006) has data for 336 galaxies found in
large-scale structures across the sky near the South Celestial Pole. The two
samples are thus independent. Therefore, Fairall started his numbers for his
latest large-scale structure sample at 1201 to avoid confusion between it and
his earlier sample of compact galaxies.
Q:I have noticed that the RC3 data in NED sometimes do
not agree with the RC3 printed version. Which is correct?
A:NED's version of RC3 (the Third Reference
Catalogue of Bright Galaxies) includes the many corrections detailed in Corwin
AJ 108, 2128, 1994
as well as a few others made since that paper was published.