The "McNeil's Nebula" and three (four?) new variable stars close to it.

Gianluca Masi

Physics Dept., University of Rome "Tor Vergata"

                                                                                                                                                                                     Last update: 21 Sept. 2005


    On Feb. 9 2004, the International Astronomical Union Circular 8284 announced the discovery of a new nebular feature close to M78 (Ori), a well-know reflecting nebula discovered by Mechain in 1780. The author, Jay McNeil, recognized the new object while processing his own CCD images, later compared with other pictures of the area: it appeared like  a small fuzzy object few arcminutes SW of M78.

    Soon after the CBAT issued that discovery Circular I remotely used, together with  F. Mallia - on the behalf of Campo Catino Astronomical Observatory (Italy) -  the Tenagra II 32-inch reflector (AZ) to image the nebula, in order to learn more about its nature. Since the first observing night (Feb 11), a star was observed on the southern edge of the McNeil nebula, actually embedded with it. Here is the sum of 4 frames, each integrated for 60 s in the R-band, using the Tenagra II telescope. The telescope + CCD provide a scale of 0.87"/pixel.


 Thanks to the power of the telescope used, the morphology of the nebula was carefully analyzed and all the data reported to the CBAT on Feb 11

     The image above was processed to show isophotes, to better see the shape of the nebula and its extension. 


The nebula is 78" (along declination) x 57" (along RA) large.

Here is a more detailed report (the very same sent to CBAT on Feb 11, 2004):

The object was imaged on 11.16 Feb. 2004 UT by G. Masi (University of Rome "Tor Vergata") and F. Mallia (Campo Catino Observatory, Italy) using the Tenagra 32-inch reflector + CCD + a standard R filter. A total integration time of 120s was used. The whole object (including the nebulosity visible at the HH 22 position: actually, now an apparently single nebula is there, ranging from the H22 position to the bright star to the south, described below. Of course this can be just a geometric effect - H22 is not physically involved with the new object, as reported on IAUC8284) is about 70x40 arcseconds large (refined above using isophotes, ndr), elongated in the NE-SW direction. The central part of the whole nebula now visible is located at the following coordinates:

    RA: 05h46m13.5s Decl.: -00d05'45" (J2000.0, based on 30 USNOA2.0 stars, mean residuals 0.38").

The new nebula has a brighter knot at the following position, south respect toH22:

    RA: 05h46m13.0s Decl.: -00d05'55" (residuals et al as above).

A star is located on the southern edge of the nebula (apparently embedded with it) at the following coordinates:

    RA: 05h46m13.1s Decl.: -00d06'04" (residuals et al as above)

with a R magnitude around 17.5 (assuming for the reference stars their USNOA2.0 red magnitudes; revised below using the filed photometry provided by A. Henden, ndr).

SIMBAD gives the following position for the IRAS 05436-0007 source:

    RA: 05 46 14.0 Decl. -00 06 01 (J2000.0)

SIMBAD, also, provides the following J2000.0 position for HH 22:

    RA 05 46 14.2 Decl. -00 05 31 

   In the meanwhile, I started a research on the web, looking for M78 images. As that is a very famous Messier object, there are so many images around showing it, together with its neighbors. In other words, it was possible - in principle - to investigate the new object using old material. After a number of efforts, it turned out that the McNeil Nebula started to be visible in Nov. 2003, continuously increasing its brightness till Jay found it. All the other images does show nothing obvious... with an important exception. In fact, I noticed that the SEDS website showed an image of M78 where the McNeil nebula was easily visible as today. It was grabbed by Evered Kreimer on 22 Oct. 1966, using a 12.5-inch Newtonian and a Tri-X film from Arizona (the image was included in the book "The Messier Album", John H. Mallas and Evered Kreimer, Cambridge University Press, 1978). I reported that to CBAT on Feb 10. The box in the bottom-left shows an enlargement of the feature.



     Thanks to the finding above, it is easy to conclude that the star embedded with the nebula is variable, as expected. It resembles the FU Ori type.

    The object was followed-up by me and Mallia for few nights, recording its brightness changes. Here are its R-band magnitude estimates (using a 6" aperture, unless otherwise noted):

Feb 11.16 2004 UT  R = 16.5
Feb 14.15 2004 UT  R =
Feb 16.14 2004 UT  R =
Feb 18.14 2004 UT  R =
Feb 20.10 2004 UT  R =
Feb 25.12 2004 UT  R =
Feb 25.13 2004 UT  V = 18.4  (5" aperture, being the star faint in V; measuring R with the same aperture, I get the following V-R=1.6)

On 19 Feb. 2004, the CBAT issued the IAU Circular n. 8290 reporting all my findings mentioned above.

The animation at the beginning of this page shows the variation between Feb. 13 and 16.

The star has been officially named V1647 Orionis.


    March 2005: updates. The nebula and the involved star (1647 Ori) were observed again in late-2004 and 2005, this time using the SoTIE telescope, with the collaboration of Roger Wilcox (TIE) and Franco Mallia (Campocatino Observatory). Using these images, I have been able to show how the star was brighter on Sept. 2004, while definitely fainter on March 2005. While unfiltered (but grabbed with the very same setup), I used the images to estimate the star brightness, using standard R mags for the reference stars.

18 Mar 2004: 16.15  unfiltered
14 Sep 2004  15.90  unfiltered
16 Mar 2005  16.60  unfiltered
 7 Sep  2005   16.80 unfiltered  ** observations performed using the SoTIE telescope under excellent sky conditions **

    The nebula faded accordingly. The object will be observed again during the remaining season.

        As for the observations performed since Sept. 2004, I wish to thank the NASA/TIE team (in particular Roger Wilcox for operating the scope while I observed), as well as Software Bisque, for their support and disposability. I also thank Carnegie Observatories and  Las Campanas Observatory for hosting the SoTIE telescope in Chile


AND NOW ANOTHER STORY: Three (four?) new variable stars close to McNeil's Nebula


    At some point, on 16 Feb. 2004 I spotted a previously unknown variable object about 2' E from the McNeil's nebula. The variable is marked by two white lines.


     Measures on four nights showed it fluctuating of about 0.5 mag in the R-band. Below is the photometry:

Feb 11.16 2004 UT  R= 14.91
Feb 13.12 2004 UT  R= 14.97
Feb 14.15 2004 UT  R= 14.78
Feb 16.14 2004 UT  R= 14.43
Feb 18.14 2004 UT  R= 15.1
Feb 20.10 2004 UT  R= 14.99
Feb 25.12 2004 UT  R= 15.24
Feb 25.13 2004 UT  V= 16.51

    Probably, this is a T-Tauri variable (a pre-main sequence object).

    Updates.On March 23 2005, while analyzing some images grabbed with the SoTIE telescope - Chile - in collaboration with Roger Wilcox and Franco Mallia, I spotted two apparently unknown variable stars, with a further suspect. The are quite faint, but their variations is firmly confirmed (the third suspect needs more observations). All the objects are not present in GCVS and IBVS archives. Here are the positions of the sources, which I called SoTIEvar001, 002 and 003:

SoTIEvar001  05 46 10.28 -00 00 06.1
SoTIEvar002  05 45 56.70 -00 00 25.0
05 46 09.61 -00 03 30.4 ?? uncertain. ** Observations from Sept. 2005 show that this is variable for sure. **

    At the moment I cannot say more about them: these maybe T-Tauri stars, but I  need to learn more about their behaviour. Observations from Sept. 2005 confirm the variability of all the S1, S2 and S3 sources. So, it is time to plan a better follow*up to properly show what kind of variables they are.

    Star chart. I provide a simple chart, where I marked the objects mentioned in this page. MC is the McNeil's Nebula (see how its brightness evolved from Mar. 2004 to Mar. 2005), MA the variable star I reported on Feb. 2004, while S1, S2 and S3 are the new objects. 


        Again I wish to thank the NASA/TIE team (in particular Roger Wilcox for operating the scope while I observed), as well as Software Bisque, for their support and disposability. I also thank Carnegie Observatories and  Las Campanas Observatory for hosting the SoTIE telescope in Chile



Other pages featuring the McNeil's Nebula which is worth to check:


    This page will be updated once new data will be available.                             Last update: 21 September  2005