A General Catalogue of Herbig-Haro Objects

Bo Reipurth

Electronic Version 1994-1

Abstract

A catalogue of all known Herbig-Haro objects is presented. For each object is given its HH number, previous designations if any, a position, the most probable energy source, and the region and distance. Additionally, extensive notes give a brief description of each object with detailed references to the literature. The catalogue will be updated on an approximately yearly basis.


This catalogue will not be published in any journal. It is available through anonymous ftp to ftp.hq.eso.org under directory /pub/Catalogs/Herbig-Haro, which contains, in addition to a readme file, the three files: catalogue.tex, notes.tex, references.tex.

Reference to this catalogue should be done as follows:
Reipurth, B.: 1994, A general catalogue of Herbig-Haro objects,
electronically published via anon. ftp to ftp.hq.eso.org, directory /pub/Catalogs/Herbig-Haro.


Introduction

Two catalogues of Herbig-Haro objects have previously been published. George Herbig's A draft catalog of Herbig-Haro objects from 1974 gave positions, finding charts and a brief description of all 43 objects known up to that time. This was followed by A working catalogue of Herbig-Haro objects by von Hippel, Burnell, Williams (1988), which gave positions, proper motions, radial velocities and spectral information for 89 HH objects or groups of HH knots, although more HH objects were known at the time. Since then the increasingly common use of large-field CCD detectors with interference filters have caused an almost explosive development in the discovery rate of HH objects, which now number approximately 250 objects.

In the days when discoveries of HH objects were rare and only few people worked in the field it was possible to assign consecutive HH numbers to the objects as they became known. This has long since become impossible, and lacking some sort of coordinating facility, newly discovered HH objects have been given a great variety of names (e.g. S140/HH3, GGD 34, N2264 HH 14-4, RNO 40E, WSB 47, Re 4 head, GN20.18.3/HH, Th 28, HHG33.3+0.2).

About two years ago I was approached by Dr. M.-C. Lortet of the IAU Nomenclature Committee, who asked me if something could be done to bring order to this wild growing subject. After some hesitation I embarked upon a survey of the entire literature on Herbig-Haro flows with the aim to produce a complete catalogue of all known HH objects, and the result is presented here. The philosophy is closer to that of Herbig's 1974 catalogue than to that of the von Hippel, Burnell, Williams 1988 catalogue. The present catalogue contains three parts. First, a table listing for each object an HH number, any previous designations, a position, identification of a suspected driving source, the name of the general region of the object, and a distance estimate. Second, a note section where each object is briefly described and extensive and as complete as possible references are given to the literature. Third, a section with references, where also the title is listed, to help give a first idea about the content of a paper. The catalogue is thus less a source of information, and more a tool to find information.

All known HH objects accepted as such now have an HH number, in continuation of the already existing HH numbers assigned by Herbig and others. In most cases this is a great improvement over previous designations. In a few cases well known and beloved names have been sacrificed, with regret, for the sake of the larger vision of having once and for all a single nomenclature system that gives a complete description of an increasingly important class of astrophysical objects. When an object had to be renamed, a special effort was made to find a number that, whenever possible, was somehow related to the previous name. Thus RNO 40 and 43 are now HH 240 and 243, Th 28 is HH 228, M16-HH1 is HH 216, the M42 objects HH 1-10 are HH 201 - 210, GGD34 is HH 234, etc. Hopefully any transition difficulties will be shortlived.

A statistical analysis of the entire material presented here is presently being carried out, and will be published separately.

What is an HH object (and what is not)?

In the course of this work, the question has inevitably arisen a number of times whether a certain object should or should not be included in the catalogue. While it is impossible to make very strict rules for what to include, at least a set of guidelines have been set up. HH objects are small-scale shock regions intimately associated with star forming regions. They have characteristic spectra which set them apart from photo-ionized regions. The best way to unequivocally identify a nebulous object in a star forming region as an HH object is to take a spectrum. Increasingly, however, a simpler technique is used, namely to take CCD images through a [SII] interference filter and through either a similar slightly blue- or red-shifted filter that avoids the [SII] lines or through a red broadband filter around 0.9 or 1.0 µm that transmits only few and weak HH lines. If the object observed appears strongly in the [SII] filter, but not in the other filter then it is virtually certain that the object is an HH object. However, this method becomes questionable if applied in regions away from molecular clouds and known star formation activity.

Another technique, pioneered by Solf, is to place a long slit on a young star at a variety of position angles. Very short HH flows, that would be difficult to see in a direct image where the brightness of the star could swamp it, will appear clearly after elimination of the stellar continuum. I have used the guideline that such flows that extend more than several arcseconds from a star, and which could thus in principle be studied morphologically using proper coronagraphic techniques, are included in the catalogue. Stars with HH emission lines but no appreciable extent have not been included.

With the advent of infrared imaging detectors, many HH objects have been found to emit significantly in H_2 and [FeII] with roughly similar morphologies at optical and infrared wavelengths. A number of molecular hydrogen objects have been detected in embedded molecular outflows with no optical counterparts. While it seems probable that these objects differ from ordinary HH objects only in the amount of extinction along the line-of-sight, much work on the infrared properties of HH flows remains to be done before it can be justified to expand the definition of HH objects to include all objects only detected in the infrared. However, this rule can be relaxed where there is additionally strong morphological support for classification as an HH flow. Thus, in this catalogue two objects, HH 121 and HH 211, have been included which are well collimated bipolar flows, located in regions of star formation and up to now only detected at infrared wavelengths.

In recent years an increasing number of shocked regions have been found in association with evolved stars. Kinematically and morphologically these objects do not appear to differ much from Herbig-Haro objects, but spectroscopically they are rather different because the shocks occur in highly processed material. From the point of view of hydrodynamics and shock physics these objects are undoubtedly as interesting as HH flows and supernova remnants and other supersonic flows. However, the most important aspect of the Herbig-Haro phenomenon is arguably the unique insights which it has provided into the processes that lead to the formation of stars. For this reason it was felt that HH flows should remain strictly as a star formation phenomenon, as it was originally defined by Herbig and Haro. Thus, this catalogue does not contain any objects which arise from evolved stars.

Electronic publishing

Electronic publishing has two major advantages. Firstly, it allows instantaneous and worldwide distribution without the long delays inherent in normal publishing. Secondly, it allows easy up-dating as often as required. It is foreseen that new versions of this catalogue will be made available whenever substantial new information has accumulated, probably of the order of once a year. New versions will be announced in the Star Formation Newsletter.

A limitation of the present catalogue is the absence of images of the various HH objects. It is planned that one of the next versions will be made available for MOSAIC and will include images.

A cooperative effort

New bona fide Herbig-Haro objects will, as they appear in the literature, continue to be included in the catalogue. But if you have found a new HH object, you might consider to contact me when you are in the final stages of writing your paper, to find out what is the next available HH number. Unless waived, all such information will be treated as confidential and will not appear in new versions of the catalogue until your paper is accepted. Already various new objects have numbers reserved this way, so please do not simply take the next apparently free HH number as this could cause grave confusion. With a collaborative effort among the workers in the Herbig-Haro community it will be possible to establish this catalogue and its future expanded editions as a tool that will make our work easier. Your cooperation in this matter is highly appreciated.

While a major effort has been invested in making the references to work on individual objects as complete as possible, it is inevitable that some important references could be missing. Certainly not all papers mentioning a given object should be listed, and an estimate of relevance has been applied to all papers. For a little known object even a single poor observation can be helpful, but it could be irrelevant for very well studied regions like L1551. So no universal rule of inclusion can be made. If you feel that a useful reference is missing, please send an e-mail to me at reipurth@eso.org.

Accuracy of positions

The positions listed in the catalogue are taken from the literature and are as such very heterogeneous. An effort has been made to take the best available positions, but in some cases the positions are rather approximate. The equinox is 1950 and proper motions have not been considered. The goal has been to give positions that will allow an observer to point a telescope and take a CCD image and be sure that the object or an important part of it is in the field. For more details on positions, the reader must consult the references listed.

Acknowledgement

I am grateful to the following persons, who have generously given of their time to comment on this catalogue prior to publication, or have supplied information upon request: Colin Aspin, John Bally, Karl-Heinz Böhm, David Devine, Jochen Eislöffel, George Herbig, Alex Raga, Tom Ray, Luis Felipe Rodríguez, Richard Schwartz, Karen Strom, José Torrelles, Jan Wouterloot.


La Silla 30 May 1994
Bo Reipurth