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OBSID:
30078
 Title:
Confirmation of the First Helium Star Stripped by a Black Hole   
Investigator:
Ludwig
 Observer:
Ludwig, Bethany
 Phone:
4379881337
 Email:
ludwig@astro.utoronto.ca
Target Name:
SMC 981
 Sequence Number:
402423
 Instrument:
ACIS-S
 Grating:
NONE
 SI Mode:
TE_006C8
 Raster Scan:
N
 Annotated DOT:
SEP1624a

Proposal Number:
24400430
 Right Ascension:
15.2488
 Declination:
-72.6205
 Status:
archived
 Start Date:
2024-09-20 09:52:52
Category:
BH AND NS BINARIES
 Type:
GO
 AO Cycle:
24
 Dither Flag:
Y
 Y Offset:
0
 Z Offset:
0
Est. Count Rate:
5.6e-05
 Order-1 Count Rate:

 Exposure Time:
23
 Time Remaining:
22.909
 Reqd Start Time:

 Reqd Stop Time:
Period:

 Epoch:

 Start of Period:

 End of Period:

 PS Margin:

 PE Margin:

 Max Segments:
0

ACIS Mode:
TE
 Standard?:
No
 BEP Mode:
VF
 Dropped Chip Count:
0
 Optional Chips:
S1 S4
On-Chip Summing?:
No
 Row Sum:

 Column Sum:

 Frame Time:
Subarray Mode:
NONE
 Starting Row:
0
 Row Count:
1023
 Subarray Frame Time:

Duty Cycle?:
No
 Cycle Count:
0
 Primary Exp Time:

 Secondary Exp Time:
Event Filter?:
No
 Filter Threshold:

 Filter Range:

 Bias Requested?:
No
 Bias Frequency:

 Bias After?:
No
 Spatial Window?:
No

Abstract:
In a search for stars stripped of their H-rich envelopes in binaries, we have discovered a candidate stripped star - black hole (BH) system. The star appears to be an isolated, ~8Msun, helium star but radial velocities reveals an orbit of 75 days, suggesting a companion mass of >2.2 Msun. With no signs of the presence of a main sequence star in the optical spectrum, it is likely this dark companion is a BH. If true, this system would be the first discovered in a population of X-ray faint BH X-ray binaries with helium-rich donors, yielding legacy value. They are also expected to be progenitors of merging compact objects with extreme mass ratio, such as NSBH systems or the gravitational wave event GW190814. A 50ks deep Chandra exposure will reveal the true nature of this dark companion.

psci Run:
232
 Processing Date:
Sep 25 2024
 psci Directory:
/nfs/maaxnew/r3/fn/acis128c/acis128.log
OBSID:
30078
 SIM Mode:
ACIS-S
 OTG Mode:
NONE
 Seq Number:
402423
 Target Name:
SMC_981
 AO:
24
Start VCDU:
89409:040
 Start Time (UTC):
264:36921.818
 Stop Time (UTC):
264:59841.996
 Kilosecs:
22.9
 % Frames:
100.0
 # CCDs:
S4
# Frames:
7297
 # Events:
570499
 Events/sec:
24
 PSCI errors:
0
 % drops:
0.0
 Bias Errs:
0
 FP Temp:
-110.2
Parameter Block:
0x006c9034
 Window Block:
-
 # Windows:
0
 FEP Mode:
Te5x5
 BEP Mode:
F
 Start Row:
0
 # Rows:
1024
Primary Exposure:
31
 Secondary Exposure:
0
 Duty Cycle:
0
 Summing?:
No
 Bias?:
No
 Trickle?:
Yes
 Bias Run:
231

pgf@space.mit.edu Thu Apr 3 20:00:53 EST 2025