Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.

The (visible) (re-)birth of a star: IRAS 05436-0007

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 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.

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:

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 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.

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

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:

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:

  1. 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

  2. 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

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.

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.

X-ray emission from the object

Recall that Joel found a serendipitous measurement of the object back in 2002:

He requested Director's Discretionary Time on Chandra to observe it again in mid-February, after the outburst was noticed, and was granted two short exposures:

Here's a copy of the March 7 image. Notice the low signal-to-noise, since the exposure was "only" 5000 seconds.

It's clear that the new object is much brighter relative to its neighbors than it was in 2002.

The rise to peak in the optical

In mid-March, Cesar Briceno and colleagues in Venezuela announced that they had a series of images of the object showing its rise to brightness. A survey by the 1-m Schmidt telescope of Llano del Hato National Astronomical Observatory happened to scan Orion during the winter of 2003-2004.

Putting together the pieces

Let's look at the evolution of the apparent brightness of the source over the past few years. I've tried to put together all the measurements which can be compared fairly and show a detection both before and after the outburst.

Note that the source brightens by a factor of about 50 in the I-band, a factor of 20 to 30 in the near-IR, and a factor of about 100 in the X-ray.

Here's a closeup of the rise to peak and evolution afterwards:

Some missing (but existing) pieces of the puzzle:

Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.