[vsnet-chat 974] On the Subject of V&v Type I SNe Decay Parameters

["Steve H. Lucas" <76620.1721@compuserve.com>]

Supernovae Enthusiasts:

ON THE SUBJECT OF V-BAND AND VISUAL TYPE I SNe DECAY PARAMETERS. (PART I)

Over the past week I have scanned many professional articles relating to
light curves and SNe decay parameters. In addition I have dug into my own 
archives and have come up with some pleasant surprises and information
that I would like to share. These might be applied to the current "in the
air"
type I SNe that currently exist, and for future applications involving
close 
and bright SNe (ie. at the distance of the Virgo Cluster).

The research articles were written primarily by M. Hamuy, and M.M. Phillips
(plus others) in the course of an extensive study of supernovae events that
occured during the Calan/Tololo Supernovae Study (references indicated).

It might be also noted that Visual decay parameters were accessed
utilizing information gleaned from (1) Doggett & Branch, AJ., _90_,(11),
Nov., 1985, plus (2) "The Peculiar Type Ia SN 1991T" by A.Filippenko, M.
Richmond, et. al ApJ., _384_:L15-18, Jan.1, 1992.

In a paper presented by Phillips in 1993 (ApJ.,_413_,L105) a SN I decline 
decay parameter of delta m[subset] 15 (B) was introduced. This relation
defines "the amount in magnitudes that the B (blue) light curve decays in
the first 15 days after maximum light" and has been excercised rather
extensively in the Hamuy and Phillips papers from that point onward
[references 3-7, in this case]. To the _visual_ observer (amateur) this
decline parameter does not have much value. The visual observer is
involved with data that is close to the V-band. A new correlation had to be
made to assist in that band. In reference (4) the authors have indicated a
V-band decline parameter known as: delta m[subset] 20 V. Which is the 
decay magnitude of a Type I event at 20 days after maximum light
(another parameter of delta m [subset] 60 V is also used for determining
the brightness of the linear tail after the events inflection point).

As we all know the differances associated between V-band and visual
magnitudes have initiated debates and varying points of view especially
when associated with the supernovae phenomenon. As luck might have it 
an article (2) was referenced which displayed _mean_(average) templetes
for both the V-band (Leibundgut and Tammann A&A,_230_,81, 1990 using
5 normal Virgo SNe and Liebundgut et.al ApJ.,_371_,L23, 1991 involving 
18 events which were artifically converted to the Virgo Cluster distance) 
and a mean visual light curve (1).

In the templetes of V&v there is some break-away from the outset 
(immediately after maximum light) where the visual templete displays a
slightly brighter posture in relation to the V-band templete to about the 
day 20 epoch (+/- 1 day). The visual then becomes somewhat fainter
than V (following the same slope) to about day 90 (+/- 2days), where it
finally converges with the V-band slope. (Note: later time references
after this point are not readily available from my resources) 

The point of Part I of this excercise is to indicate the excellant
agreement
with the professional implementation of a decay parameter of  V/20(m)day
decline rate which can be used by visual observers at  ABOUT the same
epoch. With this in mind I will list some referenced V/20(m) parameters. It
is the hope of this author to use this excercise to obtain a useful
parameter which can be used by visual observers of bright type I SNe and
for any subsequent research associated therein.
---------------------------------------------------------------------------
-----
SN      delta m[subset]20 V parameter (reference 4)

1992bc          0.85
1991T           0.88
1992al          0.92
1992A           1.23
1992bo/1993H    1.26
1991bg          1.68

1990N           0.90
1994D           1.14

Mean visual (1) 0.95 (~)

1998aq          0.76?*
---------------------------------------------------------------------------
------
(*) This value is accessed from Dr. Kato's daily average (vsnet). A more
difinitve figure will be presented later when a "full-blown" point by point
light curve is produced, examined and fitted. At this point in time the (?)
is 
indicitive of an averaging of maximum light observations (9), which might 
have to be re-examined for a more precise fit. IMHO All observations will
also have to be re-assessed where less than 3 averages are rendered.

Part II of this excercise will deal with varying light curve speeds as
outlined in references #'s 4 and 7, utilizing the first six SN on the above
table.
**************************
References:

(3) Hamuy and Phillips AJ.,_109_ (1), Jan., 1995
(4) Hamuy and Phillips et. al, AJ.,_112_ (6),(2438-2447) Dec., 1996
(5) Hamuy and Phillips et. al, AJ.,_112_(6), (2391-2397) Dec., 1996
(6) Hamuy and Phillips et. al, AJ.,_112_(6), (2398-2407) Dec., 1996
(7) Hamuy and Phillips et. al, AJ.,_112_(6), (2408-2437) Dec., 1996

Good Hunting, and Researching

Sincerely,

Steve H. Lucas 
International Supernovae Network

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