The following document lists the file nipos.txt
from catalogue VII/239A.
A plain copy of the file
(without headers/trailers) may be downloaded.
Accurate Positions for the NGC and IC objects
These positions, along with the results of my sleuthing about the sky
(see the "puzzles solved" files on this same page), represent the core of the
work I've done cleaning up the errors and identification puzzles in the NGC
and the ICs. For each object, I've attempted to list a fair sampling of the
accurate optical (and for many, radio or infrared) positions that I can find
in the published literature of the late 20th (now early 21st) century. For
those that I can't find, I now measure positions from Digitized Sky Survey or
2MASS images using IPAC's "Skyview" software.
In general, I use the word "accurate" to mean galaxy or planetary nebula
positions with standard deviations smaller than 5 arcseconds -- down from ten
arcsec when I started this collection nearly 20 years ago. Since it is now
possible to determine positions for galaxy nuclei or central stars for
planetaries at almost any wavelength from the X-ray to the radio with standard
deviations of less than one arcsecond, I am making efforts to achieve that for
at least the new positions that I collect or measure. Thus, the positions
will be useful for multi-wavelength studies, as well as for their original
purpose here, identification.
For star clusters and the diffuse bright nebulae, the phrase "accurate
position" simply means a position good enough to unambiguously identify the
cluster or nebula. These positions sometimes need only be good to a few
arcminutes, but I try to achieve an accuracy better than that. "Precision",
the number of significant figures that I give in a position, almost always
reflects the accuracy, though with one additional digit as a round-off guard.
I've also included the original positions used in NGC and IC if a) they
are needed for identifying the objects, b) they can be said to be "accurate"
in the sense of being correct to within 10 arcseconds for galaxies or
planetaries, or c) they are accurate to within an arcminute or so for the
larger clusters and diffuse nebulae. I've also listed the old positions when
I've been unable to recover the object. In that case, they always carry the
note, "Nothing here; nominal pos." Finally, I have marked all these original
positions with an "o" in the reject column to make them easily recognizable.
Since December 2003, there have been no gaps in the position lists. All
of the NGC and IC objects have "accurate" positions, and almost all have been
looked at by a "modern" observer with the history of the object in mind. In
particular, Malcolm Thomson has extensive notes on the IC objects, Wolfgang
Steinicke has collected data for the NGC and IC objects, Steve Gottlieb is
well along with his visual observations of all the NGC objects, and I have
notes on nearly 3700 of the NGC and IC objects (the "puzzles solved" files
mentioned above).
Still to be done is a reconciliation of these several lists. Most of the
objects are labeled correctly in all the lists, but some differences remain.
There are also differences of opinion among us as to which object(s) (if any!)
a few of the numbers apply.
Here is a bit of history about measuring these accurate positions.
The southern sky was relatively better covered earlier than the north
thanks to the efforts of one man: Andris Lauberts. His ESO/Uppsala Survey of
the southern sky is a monumental work and was originally the single most
valuable source of positions for deep sky objects south of -17.5 degrees.
Among the southern objects for which he specifically searched were all the NGC
and IC objects. My own work with the de Vaucouleurs (in the Southern Galaxy
Catalogue), and with Brian Skiff (the south-equatorial extension to SGC) has
supplemented Andris's work, and has led to generally correct identifications
for the NGC objects -- particularly galaxies -- south of +3 degrees, as well
as for the larger IC galaxies, and for many other southern deep sky objects as
well. The Magellanic Clouds have been covered by several observers including
Jenni Kay, Mati Morel, and Brian Skiff. Unfortunately, not all of their work
is yet reflected here, and a thorough re-evaluation with John Herschel's
observations at hand is in order.
The northern sky was not as fortunate with respect to the NGC and ICs
until 1997 (more below). Many of the objects are too faint to be included in
the professional surveys of brighter galaxies (the CGCG, MCG, and UGC), and
the simple existence of an NGC or IC number is not in itself sufficient to
excite the interest of a professional astronomer intent on building a career
"pushing back the frontiers of science." The same is true of the many
so-called "non-existent" star clusters in the RNGC discussed by Brent Archinal
in his 1993 Webb Society monograph; they are just no longer interesting enough
to professional astronomers to merit study.
The NGC/IC position situation drastically improved in 1997 when Wolfgang
Steinicke published his "Revised New General Catalogue and Index Catalogue".
A second edition appeared in mid-1998 and has been followed by more or less
yearly updatings since. The latest that I've used is the version that
Wolfgang posted in 2001; there was another issued in April 2004 that I'll
merge into my list eventually as part of the "reconciliation" project. Using
the available literature, or the digitized sky surveys (available as RealSky
and the Digitized Sky Survey), he collected or measured accurate positions for
thousands of NGC and IC objects not previously having them. These include the
nearly 1900 positions that Wolfgang took from the Lick NPM1G catalogue. These
(and about 48,000 fainter) galaxies served as the reference frame for the Lick
Northern Proper Motion survey, so their positions are very accurately known:
standard deviations are less than 0.3 arcsec, though there is a 0.2 to 0.3
arcsec offset with respect to the ICRS -- International Celestial Reference
System -- on which the latest astrometric surveys are based. Wolfgang himself
has measured thousands more positions using RealSky or RealSky South. There
is also a systematic offset of about two arcsec in the declinations measured
using RealSkyView; these are due to a bug in the RealSkyView software. I have
folded all of these positions into my accurate position files.
The publication late in 2003 of "Star Clusters" by Brent Archinal and
Steve Hynes has at last given us a nearly-definitive list of star clusters in
the Milky Way Galaxy, the LMC, SMC, M31, and the Fornax Dwarf Spheroidal
Galaxy. I am typing in the positions for the NGC and IC clusters from this
marvelous book, starting with the LMC. Here, the positions come primarily
from Brent Archinal himself, or from a massive paper in A&AS, 84, 527, 1990
by Kontizas et al. I've called all these "open clusters" unless there is a
note that the cluster is "compact"; in that case, I call it a "globular
cluster." These "classifications" are preliminary until I can look at an
image of the cluster itself, and at its literature to find if a color-
magnitude diagram has been published. These usually pin down the
classification.
I have also merged in other large lists of optical positions for galaxies
and planetaries, including those from Brian Skiff at Lowell Observatory, Steve
Gottlieb in Albany, CA, and the extragalactic groups at Bologna, Italy
(Vettolani et al), NRAO (Condon et al), and Lyons, France (Paturel et al).
This has still left thousands of galaxies, nebulae, and clusters with
either no accurate position or only a single position. I have measured all of
these myself (on the POSS prints, the SERC films, or on DSS images downloaded
from HEASARC's SkyView web site), have extracted positions from one of the
astrometric catalogues (primarily GSC), or have adopted positions measured by
others in the NGC/IC Project as noted above.
Finally, extending the work I've done to revise the list of 195 bright,
large, and/or nearby galaxies in the Astronomical Almanac, I have made an
effort to measure very accurate positions for the few hundred brightest
galaxies using the 2-Micron All-Sky Survey (2MASS) images available through
IPAC's Infrared Science Archive web site. Though these images are at longer
wavelengths (roughly 2 microns, as the survey name indicates) than the optical
images I've used in the past, almost all the positions derived from them are
for the galaxies' bright nuclei lost to overexposure on optical sky survey
images. These nuclei are almost all coincident with the optical or radio
nuclei. The exceptions tend to be interesting systems like NGC 520, or very
inclined galaxies like NGC 4945.
Systematically, the 2MASS coordinate system is defined by ICRS. Also the
positions measured on the 2MASS images have very small standard deviations --
on the order of 0.20 arcseconds in both coordinates. The positions in the
2MASS extended source catalog (online at "http://irsa.ipac.caltech.edu/
applications/Gator/") and the 2MASS large galaxy atlas (T. Jarrett et al,
AJ 125, 525, 2003) also have very small errors, but those in the catalog are
occasionally off for large objects near the edge of a 2MASS scan, or with
superposed stars or companion galaxies. The large galaxy atlas was created
specifically to address this and other shortcomings of the automated
processing that created the extended (and point) source catalogues.
At this point, I'd better say something about NED, the NASA/IPAC
Extragalactic Database of which I am a team member. This is a database of
data and literature about galaxies, aimed at the professional astronomer.
Thus, it reflects the professional literature. However, as I note below, I
have corrected almost all of the NGC identifications in NED, but have not yet
fixed NED's IC identifications. Thus, many of NED's IC identifications are
still wrong, or are simply missing.
During the first three months of 2001, I brought the NED NGC
identifications into line with those given here (there has been some
divergence since as I have not kept NED as systematically up-to-date as my
accurate position files. If you find a difference, trust my files, not NED.
If you find a difference that is really annoying, send me a note so that I can
fix NED; I've done this several times recently). This effort grew out of
requests from NED users for the NGC numbers on objects in the Magellanic
Clouds. Most of these are star clusters, and had not been previously included
in NED. This work has also led to the resolution of many more NGC puzzles,
primarily in the south where Lauberts or Steinicke had not made positive
identifications. As I noted in the previous paragraph, I've not yet made a
systematic attempt to sort out the NED IC identifications unless those were
involved with an NGC object.
Also still in progress is a careful historical check of the positions
that I have taken from other sources: are the objects that the modern
positions point at really the ones that were found a century or two ago?
While we have made a lot of progress toward answering that question for most
of the NGC and IC objects (see the "puzzles solved" files that I, Wolfgang
Steinicke, Steve Gottlieb, and Malcolm Thomson have put together), there is
still a lot that needs to be done. Regard these position files, along with
the puzzle files, as a step in that direction.
ACKNOWLEDGMENTS
I take great pleasure in thanking several people specifically for their
help in this "informal" quest for perfection. First, my colleagues in the
NGC/IC Project who have contributed data and copies of the old literature,
furnished positions, and suggested identifications, specifically (in no
particular order) Brian Skiff, Malcolm Thomson, Wolfgang Steinicke, Bob
Erdmann, Steve Gottlieb, Brent Archinal, Chris Watson, Steve Coe, Ron Buta,
and Glen Deen. Most of these folks have also spent considerable time writing
articles or preparing speeches about the project -- getting the word out and
helping others to discover the pleasures of deep-sky work.
A special note of thanks is due to Bob Erdmann for his work on the
Project's Web site. It is through his work that the Project not just exists
on the World Wide Web, but that it has received most of the recognition that
it has. Were it not for his dedicated effort, our individual work would still
sit only in own separate file systems, scattered notes known only to a few
diehard fans of the historical sky.
Others who have done special digging in libraries and observatory
archives, or who have made contributions of positions, time, or materials
include Andris Lauberts, Brian Cuthbertson, Brian Marsden, Daniel Green, Tom
DeMary, Harvey MacGillivray, Jason Adamik, Jim Caplan, Don Osterbrock, Leos
Ondra, Yann Pothier, Marion Schmitz, Paul Brown, James Bryan, Tony Flanders,
Guiseppe Longo, Kathrine Haramundanis, Steven Dick, Brenda Corbin, Angus
McDonald, and others whom I must have forgotten -- my apologies to all who
have fallen victim to my leaky memory.
Laurent Cambresy at CDS first suggested to me that this work might find a
place in their holdings (VII/239), and Francois Oschenbein has prepared these
lists for their inclusion in the CDS collection. Francois has also helped
track down missing and obscure references that I had let go by the wayside
over the years.
Gerard and Antoinette de Vaucouleurs got me started on this quest through
their support and encouragement beginning in 1965, and ending only with their
deaths in 1987 and 1995. Their Reference Catalogues of Bright Galaxies led me
directly into the historical byways. I would also be remiss if I did not
acknowledge the extraordinary patience of my wife Kathleen who continues to
sacrifice evenings and weekends to the never-ending quest for an accurate
representation of the deep sky. Morris, Thumper, Angelica, Crabcake, Bunty,
Dante, and Nicco have also provided much-needed grounding, and have often
pulled me back to their solid feline world of food and affection, clearly the
REAL objects of earthly delight. Galaxies can sometimes, rightly, become mere
phantoms in the sky.
I should also thank all those many musicians and electronic and audio
engineers who make the great music of the past thousand-plus years available
to us at any time of day or night. We live in a special place and time ("a
glorious accident"), and we are far more fortunate than we usually acknowledge
or even realize. I'm happy now to acknowledge that, and to paraphrase, "A day
without music -- or galaxies! -- is a day without life."
Finally, here are some formal acknowledgments for the several data
services without which almost none of this work would have happened. These
are the guys who made it possible, and who make it easy.
The Sky Surveys, DSS, and STScI:
The Digitized Sky Surveys were produced at the Space Telescope Science
Institute under U.S. Government grant NAG W-2166. The images of these
surveys are based on photographic data obtained using the Oschin Schmidt
Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates
were processed into the present compressed digital form with the permission
of these institutions. [Go to http://archive.stsci.edu/dss/index.html]
The National Geographic Society - Palomar Observatory Sky Atlas (POSS-I)
was made by the California Institute of Technology with grants from the
National Geographic Society.
The Second Palomar Observatory Sky Survey (POSS-II) was made by the
California Institute of Technology with funds from the National Science
Foundation, the National Geographic Society, the Sloan Foundation, the
Samuel Oschin Foundation, and the Eastman Kodak Corporation.
The Oschin Schmidt Telescope is operated by the California Institute of
Technology and Palomar Observatory.
The UK Schmidt Telescope was operated by the Royal Observatory Edinburgh,
with funding from the UK Science and Engineering Research Council (later the
UK Particle Physics and Astronomy Research Council), until 1988 June, and
thereafter by the Anglo-Australian Observatory. The blue plates of the
southern Sky Atlas and its Equatorial Extension (together known as the
SERC-J), as well as the Equatorial Red (ER), and the Second Epoch [red]
Survey (SES) were all taken with the UK Schmidt.
HEASARC's SkyView:
We acknowledge the use of NASA's SkyView facility
(http://skyview.gsfc.nasa.gov) located at NASA Goddard Space Flight Center.
IPAC's Skyview:
This research has made use of IPAC's Skyview Image Display and Analysis
Program, developed with support from the National Aeronautics and Space
Administration. [Go to http://www.ipac.caltech.edu/Skyview/].
NED:
This research has made use of the NASA/IPAC Extragalactic Database (NED)
which is operated by the Jet Propulsion Laboratory, California Institute of
Technology, under contract with the National Aeronautics and Space
Administration. [Go to http://nedwww.ipac.caltech.edu]
IRSA (2MASS access):
This research has made use of the NASA/IPAC Infrared Science Archive (IRSA)
which is operated by the Jet Propulsion Laboratory, California Institute of
Technology, under contract with the National Aeronautics and Space
Administration. [Go to http://irsa.ipac.caltech.edu].
SIMBAD:
This research has made use of the SIMBAD database, operated at CDS,
Strasbourg, France. [Go to http://simbad.u-strasbg.fr/].
LEDA:
We have made use of the LEDA database (http://leda.univ-lyon1.fr).
ADS:
This research has made use of NASA's Astrophysics Data System Bibliographic
Services. [Go to http://adsabs.harvard.edu/ and
http://adsabs.harvard.edu/historical.html].
------------------------------------------------------------------------------
Here is an explanation of the data found in the NGC/IC accurate position
files:
1) NGC and/or IC number, preceded by "N" or "I". Up to two additional
NGC/IC numbers are also noted in this column. Other names are in the
Comments column. If there are two or more components to an object that
have not already been noted in the literature, I use directional suffixes
(e.g. "nw" is northwest, "se" is southeast, "m" is middle, etc.). I am
adding these directional suffixes to ALL the multiple objects here; my
goal is to keep confusion to a minimum.
>Note that you can enter an object's position (NOT its name) into one of
the DSS or RealSky viewers to find EXACTLY which object carries the
NGC/IC number that I've assigned. Bob Erdmann is preparing the NGC/IC
Project images in just this way.
>I've added additional suffixes for nearby companions clearly not seen by
the NGC/IC observers (usually just "comp" for "companion," though often
with a directional suffix added); and for the components of objects that
are double or triple stars. Sometimes when the stars are merged, I give
only a single position for the pair -- separate positions don't have much
meaning in these cases where the position is mainly useful for
identification. Again, my goal has been to keep confusion to a minimum.
Which leads us to ...
>Commonly-used suffixed numbers (e.g. N0078A, N0078B) are also noted here
(primarily to prevent confusion, though Bob Erdmann and I find them an
annoyance; they are also in two separate files "ngcspos.all" and
"icspos.all"). Most of these suffixed numbers come to us from three
sources: Gerard de Vaucouleurs's 1956 survey of southern Shapley-Ames
galaxies, Eric Holmberg's 1937 list of double and multiple galaxies, and
a list of galaxies in the far northern sky found by Philip Keenan, also
published in 1937. Most of these also appear in the first two Reference
Catalogues, and in RNGC. The southern ones appear in SGC and ESO. Some
of the suffixes also come from UGC, but these are relatively rare, as are
additional suffixes scattered through the literature. I've attempted to
apply the unsuffixed number to the object seen by the original observer,
but there are undoubtedly mistakes remaining -- I've not yet looked at
everything.
>There are usually only three cases where the earlier observers added the
alphabetical suffixes that we find so problematical:
1) The NGC/IC object is composed of two or more "components" (NGC 78
is an example; we are not quite sure which of these its discoverer
Pechule actually saw ...).
2) The NGC/IC object has nearby "companions" on the sky; these
are sometimes actual physical companions, sometimes just optical
superpositions of objects at different distances (most of these are
from Holmberg's 1937 thesis on double and multiple galaxies).
3) Completely unrelated objects up to a degree or more from the NGC/IC
object may bear the NGC/IC number and a suffix simply because the
NGC/IC object was the nearest "named" galaxy (most of these are
from de Vaucouleurs's 1956 survey of the southern Shapley-Ames
galaxies, or from Keenan's 1937 Astrophysical Journal paper).
The most bothersome cases arise when there are suffixed objects in two or
all three of these categories. NGC 6166 is an example. It is composed
of four merging components -- labeled "A" to "D" in a 1961 Astronomical
Journal article by Rudolf Minkowski -- and has four companions -- labeled
"A" to "D" in RNGC, but "b" to "e" by Holmberg in 1937 (N6166 itself was
"a").
>Question marks and colons are added in two different situations. First,
if I've noticed that the positions from different sources disagree, and
I've not yet had a chance to find the source of the problem, I've put
question marks on the numbers. Second, if I have done the digging in the
historical literature and am still unable to reliably assign the NGC/IC
number to the correct object on the sky, I put colons and question marks
on to indicate this. These objects will usually have "stories" in the
"ngcnotes" and "icnotes" (the "puzzles [not always] solved") files. I'm
working on those that don't yet have written-out explanations. If your
particular questionable object is not yet covered, drop me a line -- I'll
pop it up in the queue for you.
2) and 3) RA and Dec for B1950.0. Precision given is usually that in the
published source, though some early entries from e.g. RC2 have been
truncated to more realistically reflect accuracy. The format is
HH MM SS.ddd, +-DD MM SS.dd (number of places to the right of the decimal
points varies); HH MM SS, +-DD MM.d; HH MM.d, +-DD MM; or HH MM, +-DD.d.
>Accuracy is another matter. Since most of the positions are from sources
other than my own work, I can't guarantee that they are accurate. On the
other hand, I don't see much point of including positions here if they
aren't accurate, so I check everything as carefully as I can when I put
positions in. In general, the positions are accurate enough to identify
the correct objects -- and as I said above, I'm trying to make them much
more accurate than that.
>I also make mistakes now and then. If you find one, please let me know
so that I can fix it -- if I don't know about it, I can't fix it.
Thanks!
4) "R": Rejected positions are noted with an asterisk "*", and original
positions from the source papers with a lower case "o", in this column.
>Positions are rejected if they differ significantly from the mean of the
other positions, or if they are known to be incorrect from other
considerations.
>The lower case letter "o" is used to flag positions from the original
lists even when they have accuracies that match modern positions. While
these may be very accurately measured, the system of reference stars in
use at the time was not as well-defined as it is now. Recovering the
positions of these reference stars at the earlier epochs is not easy,
though proper motions are now (November 2004) known for most of them,
thanks to Tycho-2 and UCAC.
>Very precisely specified declinations overlap into this column once in a
while. This last digit is preserved only as a roundoff guard digit; few
positions for extended sources are known with sub-milliarcsecond
accuracy, though I have included radio positions for galaxies (e.g. NGC
5128) with compact nuclei which are part of the definition of the ICRS
which replaced FK5 in the 1990's.
5) "So" is the source code. These are decoded in the "sources" file which
also gives my own initial ideas about the accuracy of a source, and other
relevant notes about identifications, number of positions given, etc. At
the moment (November 2004), all the source codes have entries in the
"sources" file, thanks to Francois Oschenbein who listed the missing ones
and helped me track them down.
6) "n" is the number of observations taken from the original source. This
is usually the number of individual observations going into the final
number, but is sometimes difficult to determine (some observers give the
number of nights on which observations were made; others give the actual
number of observations made per night; some have different numbers for
right ascension or declination; etc). If no number is given, n = 1.
7) Comments, Notes, and/or Remarks are entered when needed. The column
extends as far as necessary, and currently stretchs to at least column
173.
>Objects other than galaxies have their types noted in the first several
columns of this field:
GC = globular cluster
OC = open cluster
PN = planetary nebula
BN = bipolar nebula
DN = diffuse (bright) nebula
EN = emission nebula
RN = reflection nebula
HII = HII region
SNR = supernova remnant
SA = stellar association
SC = star cloud
These may be missing for objects that I've not looked at recently; I'm
filling them in as I go. They are also used in combination if needed
(e.g. N1893=I0410 is a "DN+OC").
>If the NGC or IC number applies to only part of an object, I either
append a "p" to the type (e.g. NGC 650 and NGC 651 are both "PNp"), or
attach a note explaining the situation (e.g. NGC 3189 is the southwestern
part of NGC 3190, and NGC 6960 is part of the Veil Nebula, an SNR).
>If the object is in another galaxy, that galaxy name is appended to the
type (e.g. NGC 152 is a "Cl,SMC" -- a cluster in the Small Magellanic
Cloud). The types in the Magellanic Clouds are from the same sources as
the position (but see my note above about the LMC types from "Star
Clusters" by Archinal and Hynes); they often disagree among themselves,
and with the types from other lists. Note that the young "globular"
clusters in the LMC are simply called "GC"; they are morphologically
indistinguishable from the old, red globulars. Many types from ESO are
just the first two letters of the "classification" from the ESO catalogue
(e.g. "Em" = "Emission nebula"). I'm fixing these as I see them, but
it's slow going.
>Stars, double stars, and triple stars are noted by asterisks, one per
star. Asterisms with more than three stars are usually noted "n sts" or
"n stars", where "n" is the number of stars. If two stars are widely
separated, they are sometimes noted "2 sts" or "2 stars".
>Comments are usually -- but not always! -- from the original sources; my
own notes are in square brackets when appended to a note not written by
me.
>Many cross-identifications into modern catalogues are in this column,
too. I've put in the cross-ids when I've had them in front of me.
Unless they are needed to help identify an object, I've generally not had
them handy, so many aren't here. NED, LEDA, and SIMBAD are still the
best places to find cross-id's (at least for the NGC objects): use one
of the positions listed here with a "Near Position" search.
>Some of the cross-ids are simply numbers; prepend the source code to
these (e.g. VCC 456, GSC 01234-05678).
>Occasionally, I've included some data here (e.g. galaxy types, diameters,
or magnitudes), but these are unusual. Check Wolfgang's, Steve's, or
Malcolm's lists for data.
>Abbreviations are generally taken from the NGC, but I've used "sts" for
"stars", "deg" for the degree symbol, and a few other non-standard ones.
Since these are 7-bit ASCII files, I'm limited to the characters
available on a standard US keyboard. As I use and add to the files, I'll
try to remember to mention other unusual abbreviations here.
Here is a short example of the tables with the format shown:
NGC/IC RA (1950.0) Dec (1950.0) R So n Comments, Notes, etc.
(1) (2) (3) (4)(5)(6) (7)
<------------------><------------><----------->|<--><> <------------------------------------------------------------------------------------------------------------------->
N7812 00 00 21 -34 30.8 SGC
N7814 00 00 41.1 +15 52 03 DC
N7808 00 00 58.6 -11 01 24 SPC
N7808 00 00 58.7 -11 01 21 SPC
N7816 00 01 15.2 +07 12 03 DC
N7817 00 01 24.9 +20 28 18 DC
N7813=I5384 00 01 35.7 -12 15 46 SPC 2
N7813=I5384 00 01 35.7 -12 15 46 *KET2 = Mark 0936
N7819 00 01 50.4 +31 11 43 DC
N7820 00 01 56.7 +04 55 13 DC
N7823 00 02 15 -62 20.4 SGC
N0015 00 06 27.89 +21 20 46.6 GSC 2
Harold Corwin
November 2004
© UDS/CNRS