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AAVSO Alert Notice 301

THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
25 Birch Street, Cambridge, MA 02138 USA
INTERNET: aavso@aavso.org
Tel. 617-354-0484 Fax 617-354-0665

AAVSO ALERT NOTICE 301 (May 21, 2003)

SUBJECTS: 1041-59 ETA CAR; 2349+56 RHO CAS

OBSERVATIONS REQUESTED: 1041-59 ETA CAR and 2349+56 RHO CAS

EVENTS: Possible optical brightening of eta Car over next few months; Possible optical fading of rho Cas over next few months

Visual, photoelectric, and CCD observers are strongly urged to observe these two stars closely over the coming months, as astronomers anticipate possible significant activity in each of them.

1041-59 ETA CAR
Eta Car (type S Doradus) is a very supermassive (perhaps 100 solar masses), Luminous Blue Variable that historically has shown two types of irregular eruptions - a typical S Doradus-type eruption with a brightening of 1-2 magnitudes in visual wavelength and a duration of years, and a "giant eruption" that shows a significant increase in total luminosity (to that rivaling a supernova) and mass ejection of a solar mass or more. Eta Car has experienced several of these giant eruptions, the most recent being in the 1840's when the star reached magnitude -1 and much of the material we see as the surrounding Homunculus nebula was ejected (Humphreys et al., Publ. ASP, 111,1124 (1999)).

The 5.52-year x-ray eclipse cycle believed to exist in the extremely complex eta Car is expected to produce an x-ray eclipse in late May or mid-July (depending on the model) of 2003. Optical brightening should most probably follow this eclipse, as may be seen in the 1997-2000 visual observations in the AAVSO International Database (http://www.aavso.org/adata/curvegenerator.shtml).

The present x-ray behavior (see current RXTE x-ray light curve at URL: http://lheawww.gsfc.nasa.gov/users/corcoran/eta_car/etacar_rxte_lightcurve/) and very gradual optical brightening reported to the AAVSO by observers indicate that the x-ray eclipse and subsequent optical activity may be about to occur. The multiwavelength observing campaign organized for eta Car is detailed by Dr. Michael Corcoran at the URL: http://lheawww.gsfc.nasa.gov/users/corcoran/eta_car/2003.5/ .

An article on eta Car will appear in the July 2003 issue of Sky & Telescope, which will be at newsstands very soon - this month.

Visit the AAVSO webpage on eta Car for more images, links, and more information at URL: http://www.aavso.org/etacar.shtml.

Observers should be aware that NSV 4922 (HIP 52102, HD 92397) on the AAVSO eta Car 'b' chart has a high proper motion (Hipparcos proper motion values:

R.A. = -14.29 +/- 0.88 milliarcseconds/year,
Dec. = +0.79 +/- 0.74 milliarcseconds/year).

2349+56 RHO CAS
Rho Cas (type semiregular) is a hypergiant star and one of the most luminous stars in our galaxy. Eruptions on these very rare, very massive stars produce huge mass ejections evidenced by dramatic spectral changes and optical dimming (an ejection in 2000 amounted to 10,000 Earths worth of material and caused a ~1.5-magnitude drop in visual brightness). Understanding hypergiants can help answer fundamental questions related to maximum stellar mass limits.

Astronomers are anticipating possible major activity in rho Cas over the next few months. Spectra of rho Cas show that its hydrogen lines have brightened, which indicates the probable onset of an eruption leading to mass ejection and consequent optical fading. This pattern was seen in the last months of 2000, and astronomers feel that the eruption projected for the coming months may be stronger than the 2000 one.

An article on rho Cas will appear in the July 2003 issue of Sky & Telescope to be at newsstands this month.

A summarized description of the 2000 eruption appears in AAVSO Photoelectric Photometry Newsletter, vol. 22, no. 1 (http://www.aavso.org/committees/pepnewsletter/jan03.stm).

A press release by A. Lobel et al. may be found at (http://www-cfa.harvard.edu/press/pr0302.html).

Visit the AAVSO webpage on rho Cas for AAVSO visual and photoelectric light curves, links, and more information at URL: (http://www.aavso.org/rhocas.shtml .

COORDINATES (2000):
ETA CAR -

R.A.: 10h 45m 03.59s
Decl.: -59o 41' 04.26"

RHO CAS -

R.A.: 23h 54m 23.03s
Decl.: +57o 29' 57.78"

AAVSO CHARTS: ETA CAR - REVISED (May 2003) 'a' and 'b'; NEW 'e' scale (for CCD observing)

RHO CAS - 'a' scale chart; Photoelectric Photometry chart

REPORT OBJECTS TO THE AAVSO AS: 1041-59 ETA CAR; 2349+56 RHO CAS

Monitor eta Car and rho Cas closely - every night. If you see any significant change in the brightness - more than 0.2 magnitude - please inform us here at Headquarters so we may immediately let our colleagues know of the brightness change.

CURRENT MEAN VISUAL MAGNITUDE FROM THE AAVSO INTERNATIONAL DATABASE:
ETA CAR - 5.2
RHO CAS - 4.7

SUBMIT OBSERVATIONS TO THE AAVSO

We encourage observers to submit observations via our web site (online data submission tool WebObs), or by email in AAVSO format to observations@aavso.org. If you do not have AAVSO Observer Initials, please contact Headquarters so we may assign them to you. The answering machine at AAVSO Headquarters is on nights and weekends; use our charge-free number (888-802-STAR = 888-802-7827) to report your observations, or report them via fax (617-354-0665).

Many thanks for your valuable astronomical contributions and your efforts.

Good observing!

Janet A. Mattei
Director

Elizabeth O. Waagen
Senior Technical Assistant

Keywords:
AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484