#  The Ph.D. colloquium by Sumin Tang: Exploring the Long-term and Extreme Variability of Stars 

 



####  calendar\_today Date and Time 

 **May 2, 2012** 

 10:00AM - 11:30AM EDT 

 



 

**The Ph.D. colloquium by Sumin Tang**

**Talk Title**: Exploring the Long-term and Extreme Variability of Stars  
**Location:** Phillips Auditorium

Following her colloquium, Sumin will defend her thesis in the same room.

**Abstract**: Exploring the Long-term and Extreme Variability of Stars

Stellar variations over decades are poorly explored. With the unique 100 yr coverage of DASCH (Digital Acess to a Sky Century@Harvard), for the first time, we are able to study the variable sky over long timescales in a systematic way. I have discovered exciting new types of long-term variables, which do not match any of the common classes. The most interesting one to date is a peculiar 10-yr nova. With P=119 days, it is interestingly located in the gap region between classic novae and symbiotic novae. The most probable explanation of the outburst is Hydrogen shell-burning on the WD without significant mass loss, which suggests a promising new channel for Type Ia Supernovae (SNe). We have found peculiar long-term K giant variables with 1-2 mag slow variations over decades. Most of them show strong Ca H&K emission, and 5 of them are covered by Kepler and show (in 4 stars) star spots and flaring activities. This suggests that the mysterious long-term variations may be related to strong star spots and magnetic activities which may be a new mechanism for dust formation or ejection. We discovered a 5-yr dust accretion event in KU Cyg, which is probably linked with its accretion disk. I conclude my thesis with the DASCH-Kepler variable catalog. Compared with the ASAS variable catalog, I recovered most of large amplitude variable stars (>0.5 mag). Other post-thesis discoveries include an Epsilon Aurigae-like object, and a new class of CV with stellar magnetic cycle driven accretion.



 

 



 

 See also:- [ PhD Colloquium ](/filter_by/phd-colloquium)
 
 

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