LPV Humps

LPV Humps

I can often be found, most evenings in the AAVSO chat room. If you want to chat about this project or any other facets of variable stars please stop by any evening and talk with the people on chat! https://www.aavso.org/chat

• SFRA Frank Schorr - fschorr at comcast dot net
• Special thanks to MDW Walter MacDonald
• Special thanks to Neil Butterworth

Introduction:

I started this project for the learning experience and to delve deeper into the aspects of the  "humps" on light curves of various LPVs I noticed while observing.  At this point this is not a "scientific" project but a project to create a list or "catalog" and gather more information on LPVs that show this particular type of behavior to see if there is a reason to start a scientific "project" to discover more about this type of behavior.  I hope to collect data that might be helpful to a researcher. These "humps" or "bumps" seem to mostly appear on the rising portion of LPV's light curve as seen in the light curve of the 900 day light curve of RU HER above.  A "hump" is a spot on the light curve where the slope of the curve is altered to make it look like the brightening (or dimming) of the LPV "stalls" for a period of time sometimes also called "stalling" or a "shoulder".

On some of these stars the brightness (or dimness) reverses direction giving the impression of an early maxima or even a double maxima for that cycle.  This may or may not be related to the "double" or "dual" maxima behavior of some "LPV" stars.

At this time I am focusing my energies on my favorite target S ORI and any of the "hump" LPVs that can give me data for it's full cycle such as T Cas, W Cas, S Cas, T Cam, R Aur, V Cam, R Lyn, T Umi, WZ Dra, ST Cyg, T Cep, S Cep and CT Laq. I would argue that perhaps the most interesting parts of the light curve for these stars are at the maxima at the beginning of the LC (light curve) cycle, the part of the LC leading into the start of the "hump" event, the time of the "hump" event itself, and the LC as the "hump" event ends. At this time I would think one observation a day is the proper cadence of observations to be able to gather the most useful information.

3/16/2016 Just finishing up a very detailed @250 day look at the latest "hump/stall" event for S Ori which included images from 7 AAVSONET telescopes and data from my own observatory.  I did a number of "time series" studies at various points in the ascending light curve at the times the "hump" started and ended.  Hopefully I can get an article started soon talking about my experiences.

One of the most exciting things I've read recently is a massive project done by Tomas Karlsson (KTHA) that provides detailed O-C diagrams for hundreds of Mira LPVs.  This remarkable effort can be viewed at http://var.astronet.se/mirainfooc.php.  He also provides major information for the "period length over time" for this same set of Mira stars. This data is available at http://var.astronet.se/mirainfoper.php Along with this other data he provides the mean light curves for this same set of Mira LPVs. These mean light curves are particularly exciting for me as they seem to show "the humps" on the mean light curves for many of the Mira LPVs shown.  This may mean that Tomas's data might be able to be used to show which Mira LPVs currently show this hump behavior.  This exciting data can be viewed online at http://var.astronet.se/mirainfomax.php.

Classification attempt

In N. D. Melikian's paper, "Classification of the Light Curves of Mira Variables" (Astrophysics, Vol. 42, No. 4, 1999), Melikian puts forth arguments to classify the light curves of Mira variables based on the "shape" of their light curves.  Mira stars that have a purely sinusoidal shapes would be "simple" light curves and Mira stars that have very complicated light curves, often with "hump" on the ascending (or decending) light curve including potential dual maxima.

• The period-spectrum correlation for the "complicated Mira" stars is weak or non-existant.
• The period distribution of stars with the 'complex' light curves the maximum in the period distribution was
       350-400 days while just 250-300 days for the Miras with 'simple' light curves.
• Absolute bolometric magnitudes tended to be higher in the Miras with 'complex' light curves
• According to Melikian, polarimetric observations of a group of Mira variables that contained both 'simple' and
       'complex' light curves,  50% of the 'complex' light curve stars found polarization which was over twice as much
       of the Miras with 'simple' light curves.

He felt there was a real difference in the light curves based on the shape of their light curves.

Some astronomers have said that all MIRAs have "humps" at one time or the other.  Perhaps this happens at different times as they grow older?

Measurement attempt

A paper published in Astrophysics, Vol. 50, No. 1, 2007, titled  "VARIABILITY OF LONG-PERIOD PULSATING STARS. III. CHANGES IN THE PARAMETERS OF HUMPS AT THE ASCENDING BRANCH" by V. I. Marsakova and I. L. Andronovmay have answered a lot of the questions I have concerning the "humps".  The paper can be found at http://www.springerlink.com/content/q82910824434n110/.  Thanks to James Bedient for this information.

There are two more papers in this series that talks about the methods used to produce the data in the above paper:

     Variability of long-period pulsating stars. I. Methods for analyzing observations
       http://www.springerlink.com/content/n611125846588r70/

     Variability of long-period pulsating stars. II. Additional parameters for classifying stars 
       http:www.springerlink.com/y03752753h358375

I may use a subset of the measurements mentioned in these three papers.

My project

Discovery/Identification:

• I sampled the light curves for about 450 LPVs using data for the last 15 years from the AAVSO
  International database and the ASAS1, ASAS2 and ASAS3 databases and visually inspected their
• light curves.
• So far 77 LPVs that appears to have "hump" events - please see Table 1 below
• 5 or so possible candidates - Please see Table 2

Table 1:

List of 77 LPVs that show distinct "humps" and/or double maximas since 2000 (or earlier). 

Please click on the star name to see a light curve for that star and possible other data if available.  

Table 2
Below is a table of LPV hump stars candidates and other "Dual-Maxima" project stars.

Classification/Description:

Some ideas:
  
- Accurately measure the time from the Maxima at the beginning of the cycle to the Maxima at the 
end of the cycle for each LPV that shows hump event.  Accurately measure each period for that LPVs 
for all cycles (get the period of the cycle).  If a particular cycle does not have a "hump" in it compare 
it's period to the period of a cycle with a "hump" event to see if this affects the cycle period.
R
- Measure the time from the Maxima at the beginning of the cycle to the beginning of "hump" event to 
understand how far into each cycle the "hump" event starts and the relationship of the start of the event 
from the beginning Maxima to the length of the overall cycle.  Compare this value between cycles for 
the same LPV

- Measure the time from the beginning of the hump to the end of the hump.  Compare how the length
     of the "hump" event changes between cycles.

- Calculate the length of the "hump" event compared to the length of the period of the cycle the hump
     occurs in to see if there is a relationship.

- Calculate the length of the "hump" events between cycles to see if there is a period to the "length".

- Calculate the length of time from the beginning or one "hump" event to the beginning of the next 
     "hump" event to see if there any hidden periods in the "hump" events.

- Any other suggestions?

References and articles

Good article on Humps and Bumps: Templeton poster

Mattei, Mayall and Waagen, "Maxima and Minima of Long Period Stars, 1949-1975", AAVSO 

M.R Templeton, J.A. Mattei and L.A. Willson, "Secular Evolution in MIRA Variable Pulsations",

The Astronomical Journal, 130:776-778, 2005 August

Footnotes

Note 1 - "Fast Variations of the Mean Brightness and Other Light Curve Parameters of the Carbon
Mira-Type Star S CEP", JAAVSO Volume 27, Number 2, 1999, Pages 141-145, Vladislova I.
Marsakova. He describes in detail the "hump" on the ascending curve that this star showed for
about a half of it's studied cycles. He also reports two cycles in a rows between JD 2428250 and
242950 where the light curve becomes unstable with an almost Double Maxima look on the second cycle.

Note 2 - JAAVSO Volume 25, Number 2, 1997, page 58

Note 3 - N.D. Melikian, Astrophysics, Vol. 42, No. 4, 1999, pages 408-418 - Melikian did a study of
223 Miras with light curve information from the HIPPARCOS space telescope. No list of the stars studied
is supplied.