We present photometric and spectroscopic observations of SN 2000ch , an unusual and extremely luminous variable star located in the galaxy NGC 3432 .
The object was discovered on 2000 May 3.2 during the course of the Lick Observatory Supernova Search , at an unfiltered magnitude of about 17.4 .
Pre-discovery images obtained in 1997 , 1998 , and 2000 April show the object with R = 19.2 - 19.5 mag .
Optical spectra obtained beginning on 2000 May 6 show a smooth , flat continuum and strong , broad hydrogen Balmer emission lines at wavelengths consistent with the catalogued redshift of NGC 3432 , strengthening the association of the variable with the galaxy .
Photometric monitoring reveals a complex and erratic light curve over a time span of \sim 10 days .
Subsequent optical spectra over the next \sim 3 months continued to show strong Balmer emission lines with a mean full-width at half-maximum intensity \sim 1550 km s ^ { -1 } and a distinct red asymmetry .
A spectrum obtained 9 months after the outburst is similar to the previous spectra , but the integrated flux in H \alpha is nearly half that observed during the outburst .
The object ’ s photometric behavior , spectrum , and luminosity suggest that it is a very massive and luminous variable star and might be related to some luminous blue variable stars such as \eta 
Carinae and SN 1997bs in NGC 3627 .
The brightest apparent magnitude implies an absolute magnitude of M _ { V } \approx - 12.7 at the distance of NGC 3432 , a value which is comparable to \eta Carinae during its outburst in the mid-nineteenth century .